Live-cell visualization of excitation energy dynamics in chloroplast thylakoid structures.
Iwai, Masakazu; Yokono, Makio; Kurokawa, Kazuo; Ichihara, Akira; Nakano, Akihiko
2016-01-01
The intricate molecular processes underlying photosynthesis have long been studied using various analytic approaches. However, the three-dimensional (3D) dynamics of such photosynthetic processes remain unexplored due to technological limitations related to investigating intraorganellar mechanisms in vivo. By developing a system for high-speed 3D laser scanning confocal microscopy combined with high-sensitivity multiple-channel detection, we visualized excitation energy dynamics in thylakoid structures within chloroplasts of live Physcomitrella patens cells. Two distinct thylakoid structures in the chloroplast, namely the grana and stroma lamellae, were visualized three-dimensionally in live cells. The simultaneous detection of the shorter (than ~670 nm) and longer (than ~680 nm) wavelength regions of chlorophyll (Chl) fluorescence reveals different spatial characteristics-irregular and vertical structures, respectively. Spectroscopic analyses showed that the shorter and longer wavelength regions of Chl fluorescence are affected more by free light-harvesting antenna proteins and photosystem II supercomplexes, respectively. The high-speed 3D time-lapse imaging of the shorter and longer wavelength regions also reveals different structural dynamics-rapid and slow movements within 1.5 seconds, respectively. Such structural dynamics of the two wavelength regions of Chl fluorescence would indicate excitation energy dynamics between light-harvesting antenna proteins and photosystems, reflecting the energetically active nature of photosynthetic proteins in thylakoid membranes. PMID:27416900
Balazsi, Gabor
Cooperative dynamics of excitable systems are very important for the understanding of many natural phenomena, including perturbation propagation in the nervous system. Two theoretical systems (one subexcitable and one hyperexcitable) are studied by computational methods. It is shown that the length of perturbation propagation in the subexcitable system is maximized by spatiotemporal noise of optimal intensity. New measures are introduced to describe the synchronization of hyperexcitable systems, both for phase-attractive and phase repulsive coupling. The theoretical results are finally applied to experimental data, quantitatively showing that epileptic and normal astrocyte cultures are different from each other. The results and measures that are introduced could be widely applied in any natural system of excitable elements or oscillators.
Excited state and charge-carrier dynamics in perovskite solar cell materials
Ponseca, Carlito S., Jr.; Tian, Yuxi; Sundström, Villy; Scheblykin, Ivan G.
2016-02-01
Organo-metal halide perovskites (OMHPs) have attracted enormous interest in recent years as materials for application in optoelectronics and solar energy conversion. These hybrid semiconductors seem to have the potential to challenge traditional silicon technology. In this review we will give an account of the recent development in the understanding of the fundamental light-induced processes in OMHPs from charge-photo generation, migration of charge carries through the materials and finally their recombination. Our and other literature reports on time-resolved conductivity, transient absorption and photoluminescence properties are used to paint a picture of how we currently see the fundamental excited state and charge-carrier dynamics. We will also show that there is still no fully coherent picture of the processes in OMHPs and we will indicate the problems to be solved by future research.
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.
The effect of noise and coupling on beta cell excitation dynamics
numerical simulations. We show here how the application of two recent methods allows an analytic treatment of the stochastic effects on the location of the saddle-node and homoclinic bifurcations, which determine the burst period. Thus, the stochastic system can be analyzed similarly to the deterministic...... isolated and coupled cells has been suggested to be due to stochastic fluctuations of the plasma membrane ion channels, which are supposed to have a stronger effect on single cells than on cells situated in clusters (the channel sharing hypothesis). This effect of noise has previously been studied using...
Nonlinear Dynamics of Neuronal Excitability, Oscillations, and Coincidence Detection
Rinzel, John; Huguet, Gemma
2013-01-01
We review some widely studied models and firing dynamics for neuronal systems, both at the single cell and network level, and dynamical systems techniques to study them. In particular, we focus on two topics in mathematical neuroscience that have attracted the attention of mathematicians for decades: single-cell excitability and bursting. We review the mathematical framework for three types of excitability and onset of repetitive firing behavior in single-neuron models and their relation with...
Ruei-Yu He; Visar Ajeti; Shean-Jen Chen; Brewer, Molly A; Campagnola, Paul J.
2015-01-01
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 surfa...
Eckert, Hann-Jörg; Petrášek, Zdeněk; Kemnitz, Klaus
2006-10-01
Picosecond fluorescence lifetime imaging microscopy (FLIM) provides a most valuable tool to analyze the primary processes of photosynthesis in individual cells and chloroplasts of living cells. In order to obtain correct lifetimes of the excited states, the peak intensity of the exciting laser pulses as well as the average intensity has to be sufficiently low to avoid distortions of the kinetics by processes such as singlet-singlet annihilation, closing of the reaction centers or photoinhibition. In the present study this requirement is achieved by non-scanning wide-field FLIM based on time- and space-correlated single-photon counting (TSCSPC) using a novel microchannel plate photomultiplier with quadrant anode (QA-MCP) that allows parallel acquisition of time-resolved images under minimally invasive low-excitation conditions. The potential of the wide-field TCSPC method is demonstrated by presenting results obtained from measurements of the fluorescence dynamics in individual chloroplasts of moss leaves and living cells of the chlorophyll d-containing cyanobacterium Acaryochloris marina.
Dynamical analysis of highly excited molecular spectra
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.
Dynamic polarization effects in Coulomb excitation
In this paper we discuss the excitation of a quantum harmonic system, such as a particle bound in a harmonic oscillator potential, by means of dipole and quadrupole electric fields, focusing on effects of their interference. We obtain an exact solution to this problem with methods that date back to the ideas of Wigner. We discuss the rich class of dynamic polarization effects that are involved in such excitation processes and which are relevant to stopping theory, and electromagnetic excitation of atomic and nuclear systems
Dynamics of excitable nodes on random graphs
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.
Dynamic Characteristics of Excited Atomic Systems
The dynamics of excited atom interactions with other atoms, which often lead to associative ionization, is largely governed by stochastic diffusion of the valence electron through Rydberg states prior to the ionization. Such processes are associated with random changes of the energy state of the highly excited electron, and they are likely to influence the nuclear dynamics, especially at subthermal collision energies. Possibilities of manipulation of the chaotic dynamics of Rydberg states require a detailed exploration. For an electron in a given Rydberg state moving in a microwave field, which can be generated via interaction with another atom or molecule, there exists critical field strength, above which motion of the electron in the energy space is chaotic. Recently a way to block the dynamic chaos regime was shown, if a given Rydberg state is located somewhat above the middle between the two other states with the orbital quantum number differing by one, whereby level shifts can be controlled by employing Stark/Zeeman shifts in external DC electric/magnetic fields. The stochastic effects in collisions involving Rydberg particles, in which the initial and final reaction channels are connected via intermediate highly excited collision complexes with multiple crossings of energy levels, can be treated using the dynamic chaos approach (Chirikov criterion, Standard and Keppler mapping of time evolution of the Rydberg electron, solution of the Fokker-Plank- and Langevin-type of equations, etc.). Such approach to obtaining dynamics characteristics is a natural choice, since the treatment of Rydberg electron dynamics as a kind of diffusion process allowing one to bypass the multi-level-crossing problem, which can hardly be solved by conventional quantum chemistry methods
Macroscopic dynamics of thermal nuclear excitations
The concept of kinetic temperature as a local dynamical variable of thermal nuclear collective motion is formulated using long-mean-free-path approach based on the Landau-Vlasov kinetic equation. In the Fermi drop model the thermal fluid dynamics of the spherical nucleus is analyzed. It is shown that in a compressible Fermi liquid the temperature pulses propagate in the form of spherical wave in phase with the acoustic wave. The thermal and compressional excitations are caused by the isotropic harmonic oscillations of the Fermi sphere in momentum space. (author) 25 refs.; 2 figs
Ultrafast excited-state dynamics of isocytosine.
Szabla, Rafał; Góra, Robert W; Šponer, Jiří
2016-07-27
The alternative nucleobase isocytosine has long been considered as a plausible component of hypothetical primordial informational polymers. To examine this hypothesis we investigated the excited-state dynamics of the two most abundant forms of isocytosine in the gas phase (keto and enol). Our surface-hopping nonadiabatic molecular dynamics simulations employing the algebraic diagrammatic construction to the second order [ADC(2)] method for the electronic structure calculations suggest that both tautomers undergo efficient radiationless deactivation to the electronic ground state with time constants which amount to τketo = 182 fs and τenol = 533 fs. The dominant photorelaxation pathways correspond to ring-puckering (ππ* surface) and C[double bond, length as m-dash]O stretching/N-H tilting (nπ* surface) for the enol and keto forms respectively. Based on these findings, we infer that isocytosine is a relatively photostable compound in the gas phase and in these terms resembles biologically relevant nucleobases. The estimated S1 [radiolysis arrow - arrow with voltage kink] T1 intersystem crossing rate constant of 8.02 × 10(10) s(-1) suggests that triplet states might also play an important role in the overall excited-state dynamics of the keto tautomer. The reliability of ADC(2)-based surface-hopping molecular dynamics simulations was tested against multireference quantum-chemical calculations and the potential limitations of the employed ADC(2) approach are briefly discussed. PMID:27346684
Excited state dynamics of DNA bases
Kleinermanns, K.; Nachtigallová, Dana; de Vries, M. S.
2013-01-01
Roč. 32, č. 2 (2013), s. 308-342. ISSN 0144-235X R&D Projects: GA ČR GAP208/12/1318 Grant ostatní: National Science Foundation(US) CHE-0911564; NASA(US) NNX12AG77G; Deutsche Forschungsgemeinschaft(DE) SFB 663; Deutsche Forschungsgemeinschaft(DE) KI 531-29 Institutional support: RVO:61388963 Keywords : DNA bases * nucleobases * excited state * dynamics * computations * gas phase * conical intersections Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 4.920, year: 2013
Time resolved excitation dynamics in emeraldine base
Menšík, Miroslav, E-mail: mensik@imc.cas.cz; Rais, David; Pfleger, Jiří
2015-07-29
Highlights: • fs-transient absorption spectra of emeraldine base of polyaniline pumped at 700 nm. • Kinetic master equations for experimental data. • Formation of charge transfer states within 50 fs. Non-radiative decay (0.5 ps). • Phenyl rings relaxation (2.1 ps). • Formation of long-lived polarons (∼ns). - Abstract: Using femtosecond pump–probe transient absorption spectroscopy (wavelengths 330–800 nm), we observed and explained excited state, charge transfer and polaron state dynamics in emeraldine base form of polyaniline in dimethyl sulfoxide solution. The excited state created by a pump pulse (700 nm) in the quinoid absorption Q-band loses its initial symmetry by subsequent energy transition to a charge transfer state within 50 fs. The hot charge transfer state either recombines non-radiatively into the ground state with decay time constant 0.55 ps or transfers into a relaxed state corresponding to the relaxed phenyl geometry during ca 2.1 ps. This relaxed state shows a prolonged lifetime of about 6.5 ps before its recombination to the ground state. However, a small amount of long-lived polarons with lifetime of about 2 ns in air and with lifetime longer than 6 ns in the solution bubbled with dry N{sub 2} was detected.
Fission dynamics at low excitation energy
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.
Fission dynamics at low excitation energy. 2
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.
Dynamic hyperpolarizabilities of excited states of hydrogen
On the basis of the generalized Sturm expansion of the radial part of the Coulomb Green function, a computational method is proposed and numerical results are presented for the dynamic hyperpolarizability γ and the corrections E(4) (quadratic in the light intensity) to the quasi-energy of the ground and excited states of hydrogen with principal quantum numbers n ≤ 5 in a monochromatic light field. In this approach, the problem is reduced to the summation of well-convergent double series of the hypergeometric kind, which ensures reliable numerical results both for states with a large n, and in a wide range of field frequencies ω, including the above-threshold frequency range of (ℎ/2π)ω >> vertical bar En vertical bar (vertical bar En vertical bar is the ionization potential of the state |nlm> under investigation). We consider the frequency dependence of γ and E(4), their differences for the cases of linear and circular polarizations of the field, and the relation between their real and imaginary parts, which determine the laser field-induced corrections to the position and width of energy levels. For n = 5, the significant role of mixing the vertical bar nlm> states with different values of l by a laser field in the region of resonances on intermediate bound states is demonstrated. The linear (in intensity) corrections to the photoionization cross section for excited states are analyzed and the threshold intensity corresponding to the onset of atomic level stabilization is estimated for a number of states with n = 3 and n = 5
The photodissociation and reaction dynamics of vibrationally excited molecules
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.
Optimal Dynamical Range of Excitable Networks at Criticality
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.
Stability of excited nuclei in a dynamical simulation
We investigate the stability of excited 197Au nuclei with respect to multifragmentation using a dynamical simulation based on molecular dynamics and restructured aggregation. We focus attention on 3 kinds of excitations: heat, compression and rotation. We also study the influence of a geometrical perturbation created when a projectile drills a hole in a 197Au nucleus
Effects of cell cycle noise on excitable gene circuits
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.
Lithium. Effects on excitable cell membranes
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
Excited-state dynamics of astaxanthin aggregates
Fuciman, M.; Durchan, Milan; Šlouf, V.; Kesan, G.; Polívka, Tomáš
2013-01-01
Roč. 568, č. 1 (2013), s. 21-25. ISSN 0009-2614 Institutional support: RVO:60077344 Keywords : astaxanthin * aggregates * excited states Subject RIV: BO - Biophysics Impact factor: 1.991, year: 2013
Excitation Dynamics and Relaxation in a Molecular Heterodimer
Balevicius, V; Abramavicius, D; Mancal, T; Valkunas, L
2011-01-01
The exciton dynamics in a molecular heterodimer is studied as a function of differences in excitation and reorganization energies, asymmetry in transition dipole moments and excited state lifetimes. The heterodimer is composed of two molecules modeled as two-level systems coupled by the resonance interaction. The system-bath coupling is taken into account as a modulating factor of the energy gap of the molecular excitation, while the relaxation to the ground state is treated phenomenologically. Comparison of the description of the excitation dynamics modeled using either the Redfield equations (secular and full forms) or the Hierarchical quantum master equation (HQME) is demonstrated and discussed. Possible role of the dimer as an excitation quenching center in photosynthesis self-regulation is discussed. It is concluded that the system-bath interaction rather than the excitonic effect determines the excitation quenching ability of such a dimer.
Dynamics of excited m-dichlorobenzene
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.
Optimal control of peridinin excited-state dynamics
Chábera, P.; Dietzek, B.; Yartsev, A.; Polívka, Tomáš
Nové Hrady: Academic and University Center, 2008. s. 15. [ESF Workshop on Novel Methods in Exploring Carotenoid Excited State Dynamics. 21.09.2008-25.09.2008, Nové Hrady] Keywords : peridinin * biophysics Subject RIV: BO - Biophysics
Ultrafast Excited-State Dynamics in Biological Environments
Fürstenberg, Alexandre; Vauthey, Eric
2007-01-01
We discuss and illustrate by several examples how the ultrafast excited-state dynamics of a chromophore can be altered when changing its environment from a homogenous solution to a biological molecule such as proteins or nucleic acids.
Crowds as an Excitable Medium for Spiral Wave Dynamics
Welsh, Andrea; Greco, Edwin; Fenton, Flavio
Spiral wave (SW) patterns are studied in many physical, biological, and chemical excitable systems. Of particular importance are SW of electrical activity that develop in the heart and give rise to arrhythmias such as tachycardia (single SW) and fibrillation (multiple SWs). We investigate if a crowd of people given simple rules for activation and deactivation, modeled on cardiac cells, can act as a living simulation for SW dynamics. For group sizes ranging from 50 to 650 people we demonstrate, experimentally, the existence of stable spiral waves and of spiral wave breakup leading to chaotic dynamics. Numerical simulation predicts the simple rules lead to well define wave fronts. People, however, respond with various degrees of anticipation and misinformation. This human behavior can lead to smoothed fronts or even lead to spiral wave breakup and chaos. We present a new cell model that includes variations in reaction to account for the observed behavior in crowds. This model may be useful in the study of coupling and decoupling of cardiac cells that lead to arrhythmic behavior. Supported by NSF.
Dynamic process of free space excitation of asymmetry resonant microcavity
Shu, Fang-Jie; Sun, Fang-Wen
2012-01-01
The underlying physics and detailed dynamical processes of the free space beam excitation to the asymmetry resonant microcavity are studied numerically. Taking the well-studied quadrupole deformed microcavity as an example, we use a Gaussian beam to excite the high-Q mode. The simulation provides a powerful platform to study the underlying physics. The transmission spectrum and intracavity energy can be obtained directly. Irregular transmission spectrum was observed, showing asymmetric Fano-type lineshapes which could be attributed to interference between the different light paths. Then excitation efficiencies about the aim distance of the incident Gaussian beam and the rotation angle of the cavity were studied, showing great consistence with the reversal of emission efficiencies. By projecting the position dependent excitation efficiency to the phase space, the correspondence between the excitation and emission was demonstrated. In addition, we compared the Husimi distributions of the excitation processes an...
Fission dynamics at low excitation energy
Aritomo, Y.; Chiba, S.
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 vibrati...
Hilar mossy cell circuitry controlling dentate granule cell excitability
Seiichiro Jinde
2013-02-01
Full Text Available Glutamatergic hilar mossy cells of the dentate gyrus can either excite or inhibit distant granule cells, depending on whether their direct excitatory projections to granule cells or their projections to local inhibitory interneurons dominate. However, it remains controversial whether the net effect of mossy cell loss is granule cell excitation or inhibition. Clarifying this controversy has particular relevance to temporal lobe epilepsy, which is marked by dentate granule cell hyperexcitability and extensive loss of dentate hilar mossy cells. Two diametrically opposed hypotheses have been advanced to explain this granule cell hyperexcitability – the “dormant basket cell” and the “irritable mossy cell” hypotheses. The “dormant basket cell” hypothesis proposes that mossy cells normally exert a net inhibitory effect on granule cells and therefore their loss causes dentate granule cell hyperexcitability. The “irritable mossy cell” hypothesis takes the opposite view that mossy cells normally excite granule cells and that the surviving mossy cells in epilepsy increase their activity, causing granule cell excitation. The inability to eliminate mossy cells selectively has made it difficult to test these two opposing hypotheses. To this end, we developed a transgenic toxin-mediated, mossy cell-ablation mouse line. Using these mutants, we demonstrated that the extensive elimination of hilar mossy cells causes granule cell hyperexcitability, although the mossy cell loss observed appeared insufficient to cause clinical epilepsy. In this review, we focus on this topic and also suggest that different interneuron populations may mediate mossy cell-induced translamellar lateral inhibition and intralamellar recurrent inhibition. These unique local circuits in the dentate hilar region may be centrally involved in the functional organization of the dentate gyrus.
Superfluid 4He dynamics beyond quasiparticle excitations
Beauvois, K.; Campbell, C. E.; Dawidowski, J.; Fâk, B.; Godfrin, H.; Krotscheck, E.; Lauter, H.-J.; Lichtenegger, T.; Ollivier, J.; Sultan, A.
2016-07-01
The dynamics of superfluid 4He at and above the Landau quasiparticle regime is investigated by high-precision inelastic neutron scattering measurements of the dynamic structure factor. A highly structured response is observed above the familiar phonon-maxon-roton spectrum, characterized by sharp thresholds for phonon-phonon, maxon-roton, and roton-roton coupling processes. The experimental dynamic structure factor is compared to the calculation of the same physical quantity by a dynamic many-body theory including three-phonon processes self-consistently. The theory is found to provide a quantitative description of the dynamics of the correlated bosons for energies up to about three times that of the Landau quasiparticles.
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
Class of kick-excited self-adaptive dynamical systems: 'quantized' oscillation excitations
A class of kick-excited self-adaptive dynamical systems is formed and proposed. The class is characterized by a non-linear (inhomogeneous) external periodic excitation (as regards the coordinates of the excited system) and is remarkable for the occurrence of the following objective regularities: the phenomenon of 'discrete' ('quantized') oscillation excitation in macro-dynamical systems having multiple branch attractors and strong self-adaptive stability. The main features of the class of systems are studied both numerically and analytically on the basis of the general model of a pendulum under inhomogeneous action of a periodic force (referred to as a kicked pendulum). A diagram involving multiple bifurcations for the attractor set of the system under consideration is obtained and analyzed. The complex dynamics, evolution and the fractal boundaries of the multiple attractor basins in state space corresponding to energy and initial phase variables are obtained, traced and discussed. An analytic proof is presented showing the existence of 'quantized' oscillations for the kick-excited pendulum. An analytic approach is given applicable to the cases of small and large amplitudes (small and large non-linearity). The spectrum of possible oscillation amplitudes for the pendulum is studied as well as its motion in a rotational regime under the influence of an external non-homogeneous periodic force. Generalized conditions for the excitation of pendulum oscillations under the influence of an external non-linear force are derived. A wide spectrum of applications of the formed class of systems is presented
Dynamics of delay-coupled excitable neural systems
Dahlem, M. A.; Hiller, G; Panchuk, A.; Schoell, E.
2008-01-01
We study the nonlinear dynamics of two delay-coupled neural systems each modelled by excitable dynamics of FitzHugh-Nagumo type and demonstrate that bistability between the stable fixed point and limit cycle oscillations occurs for sufficiently large delay times and coupling strength. As the mechanism for these delay-induced oscillations we identify a saddle-node bifurcation of limit cycles.
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.
Nonlinear Dynamical Analysis for the Cable Excited with Parametric and Forced Excitation
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.
Wave packet dynamics in molecular excited electronic states
We theoretically explore the use of UV pump – UV probe schemes to resolve in time the dynamics of nuclear wave packets in excited electronic states of the hydrogen molecule. The pump pulse ignites the dynamics in singly excited states, that will be probed after a given time delay by a second identical pulse that will ionize the molecule. The field-free molecular dynamics is first explored by analyizing the autocorrelation function for the pumped wave packet and the excitation probabilities. We investigate both energy and angle differential ionization probabilities and demonstrate that the asymmetry induced in the electron angular distributions gives a direct map of the time evolution of the pumped wave packet
The damping and excitation of galactic warps by dynamical friction
Nelson, R W; Nelson, Robert W; Tremaine, Scott
1994-01-01
We investigate the dynamical interaction of galactic warps with the surrounding dark matter halo, using analytic perturbation theory. A precessing warp induces a density wake in the collisionless dark matter, which acts back on the original warp, transferring energy and angular momentum between the warp and halo (dynamical friction). In most cases dynamical friction damps the warp, but in unusual circumstances (such as a halo that rotates in the same direction as the precession of the warp, or a warp in the equatorial plane of an axisymmetric prolate halo) friction can excite a warp. The damping/excitation time is usually short compared to the Hubble time for realistic systems. Thus most warps cannot be primordial; they must be maintained by some ongoing excitation mechanism.
Dynamic Coherence in Excitonic Molecular Complexes under Various Excitation Conditions
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...
Dynamical multifragmentation of highly excited nuclear systems
In the framwork of a dynamical multifragmentation model we investigated the fragmentation of expanding nuclear systems. We found that the stable fragment mass multiplicity distribution differs (in some cases essentially) from the cluster distribution in thermal equilibrium investigated sofar. We especially investigated the pure power-law ansatz of the equilibrium distribution and we found that in certain cases the fragment distribution continues to have this form with an effective power. (orig.)
Nonlinear dynamic response of stay cables under axial harmonic excitation
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.
Toward the excited meson spectrum of dynamical QCD
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.
Optimal control of peridinin excited-state dynamics
Dietzek, B.; Chábera, P.; Hanf, R.; Tschierlei, S.; Popp, J.; Pascher, T.; Yartsev, A.; Polívka, Tomáš
2010-01-01
Roč. 373, 1-2 (2010), s. 129-136. ISSN 0301-0104 Institutional research plan: CEZ:AV0Z50510513 Keywords : peridin * excited-state dynamics * coherent control Subject RIV: BO - Biophysics Impact factor: 2.017, year: 2010
Investigations of ultrafast dynamics in electronically excited alkylbenzenes
Maksyutenko P.
2013-03-01
Full Text Available We investigate ultrafast dynamics in electronically excited states of some typical alkylbenzenes by time-resolved two-colour four wave mixing and velocity map imaging as complementary methods. In this context an upgraded double-sided time-resolved velocity map imaging setup is also proposed.
Excited State Structural Dynamics of Carotenoids and Charge Transfer Systems
This dissertation describes the development and implementation of a visible/near infrared pump/mid-infrared probe apparatus. Chapter 1 describes the background and motivation of investigating optically induced structural dynamics, paying specific attention to solvation and the excitation selection rules of highly symmetric molecules such as carotenoids. Chapter 2 describes the development and construction of the experimental apparatus used throughout the remainder of this dissertation. Chapter 3 will discuss the investigation of DCM, a laser dye with a fluorescence signal resulting from a charge transfer state. By studying the dynamics of DCM and of its methyl deuterated isotopomer (an otherwise identical molecule), we are able to investigate the origins of the charge transfer state and provide evidence that it is of the controversial twisted intramolecular (TICT) type. Chapter 4 introduces the use of two-photon excitation to the S1 state, combined with one-photon excitation to the S2 state of the carotenoid beta-apo-8'-carotenal. These 2 investigations show evidence for the formation of solitons, previously unobserved in molecular systems and found only in conducting polymers Chapter 5 presents an investigation of the excited state dynamics of peridinin, the carotenoid responsible for the light harvesting of dinoflagellates. This investigation allows for a more detailed understanding of the importance of structural dynamics of carotenoids in light harvesting
Excited State Spectra and Dynamics of Phenyl-Substituted Butadienes
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...
Transient processes under dynamic excitation of a coherent population trapping resonance
Khripunov, S. A.; Radnatarov, D. A.; Kobtsev, S. M.; Yudin, V. I.; Taichenachev, A. V.; Basalaev, M. Yu; Balabas, M. V.; Andryushkov, V. A.; Popkov, I. D.
2016-07-01
It is shown for the first time that under dynamic excitation of a coherent population trapping resonance in Rb vapours at different bichromatic pump modulation frequencies from a few tens of hertz and higher, the resonance is dramatically deformed as a result of emerging intensity oscillations of radiation transmitted through an Rb vapour cell. A significant change in the shape of the resonance under its dynamic excitation is confirmed experimentally and theoretically. A possible impact of the identified changes in the shape of the coherent population trapping resonance on the stability of an atomic clock is qualitatively discussed.
The symmetry of capacitively coupled radio frequency (CCRF) discharges can be controlled electrically by applying a fundamental frequency and its second harmonic with fixed but adjustable phase shift θ between the driving voltages to one electrode. In such a discharge a variable dc self-bias η is generated as an almost linear function of θ for 00 ≤ θ ≤ 900 via the Electrical Asymmetry Effect. The control parameter for η and the discharge symmetry is θ. Here electron dynamics in electrically asymmetric geometrically symmetric dual frequency discharges operated in argon at 13.56 and 27.12 MHz is investigated experimentally by a particle-in-cell simulation and by an analytical model. The electron dynamics is probed by the electron impact excitation rate of energetic electrons from the ground state into highly excited levels. At high pressures (collisional sheaths) the excitation dynamics is found to work differently compared with conventional CCRF discharges. Unlike in classical discharges the maxima of the time modulated excitation at the powered and grounded electrode within one low frequency period will be similar (symmetric excitation), if η is strong at θ ∼ 00, 900, and significantly different (asymmetric excitation), if η ∼ 0 V at θ ∼ 450. At low pressures (collisionless sheaths) the excitation dynamics works similar to classical discharges, i.e. the excitation will be asymmetric, if η is strong, and symmetric, if η ∼ 0 V. This dynamics is understood in the frame of an analytical model, which provides a more detailed insight into electron heating in CCRF discharges and could be applied to other types of capacitive RF discharges as well.
Dynamic Loads Generation for Multi-Point Vibration Excitation Problems
Shen, Lawrence
2011-01-01
A random-force method has been developed to predict dynamic loads produced by rocket-engine random vibrations for new rocket-engine designs. The method develops random forces at multiple excitation points based on random vibration environments scaled from accelerometer data obtained during hot-fire tests of existing rocket engines. This random-force method applies random forces to the model and creates expected dynamic response in a manner that simulates the way the operating engine applies self-generated random vibration forces (random pressure acting on an area) with the resulting responses that we measure with accelerometers. This innovation includes the methodology (implementation sequence), the computer code, two methods to generate the random-force vibration spectra, and two methods to reduce some of the inherent conservatism in the dynamic loads. This methodology would be implemented to generate the random-force spectra at excitation nodes without requiring the use of artificial boundary conditions in a finite element model. More accurate random dynamic loads than those predicted by current industry methods can then be generated using the random force spectra. The scaling method used to develop the initial power spectral density (PSD) environments for deriving the random forces for the rocket engine case is based on the Barrett Criteria developed at Marshall Space Flight Center in 1963. This invention approach can be applied in the aerospace, automotive, and other industries to obtain reliable dynamic loads and responses from a finite element model for any structure subject to multipoint random vibration excitations.
Mitigation of mode instabilities by dynamic excitation of fiber modes
Otto, Hans-Jürgen; Jauregui, Cesar; Stutzki, Fabian; Jansen, Florian; Limpert, Jens; Tünnermann, Andreas
2013-03-01
By dynamically varying the power content of the excited fiber modes of the main amplifier of a fiber-based MOPA system at high average output power levels, it was possible to mitigate mode instabilities to a large extent. In order to achieve the excitation variation, we used an acousto-optic deflector in front of the Yb-doped rod-type fiber. Therewith, it was possible to significantly increase both the average and the instantaneous minimum power content of the fundamental mode. This, consequently, led to a substantial improvement of the beam quality and pointing stability at power levels well beyond the threshold of mode instabilities.
Lattice dynamics of femtosecond laser-excited antimony
Abdel-Fattah, Mahmoud Hanafy; Bugayev, Aleksey; Elsayed-Ali, Hani E.
2016-07-01
Ultrafast electron diffraction is used to probe the lattice dynamics of femtosecond laser-excited antimony thin film. The temporal hierarchies of the intensity and position of diffraction orders are monitored. The femtosecond laser excitation of antimony film was found to lead to initial compression after the laser pulse, which gives way to tension vibrating at new equilibrium displacement. A damped harmonic oscillator model, in which the hot electron-blast force contributes to the driving force of oscillations in lattice spacing, is used to interpret the data. The electron-phonon energy-exchange rate and the electronic Grüneisen parameter were obtained.
Dynamic response of parallel resonant circuit with different power excitations
In order to avoid drawing a large reactive power from the alternating current line, the White circuit type resonant network is adopted widely as the structure of the magnet power supply system of the rapid-cycling synchrotron. Reducing the total harmonic distortion (THD)of the magnet current in the parallel resonant network is the key technique for the magnet current tracking accuracy. Based on the dynamic response analysis of a single mesh parallel resonant circuit in the paper, it shows that the continuous power excitation is of great benefit to reducing the magnet current harmonics. The paper also gives a description of our experimental studies on the dynamic response with the pulse and continuous power excitation in a parallel resonant network model. (authors)
Dynamics of a Parametrically Excited System with Two Forcing Terms
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.
Excitation energy transfer: Study with non-Markovian dynamics
In this paper, we investigate the non-Markovian dynamics of a model to mimic the excitation energy transfer (EET) between chromophores in photosynthesis systems. The numerical path integral method is used. This method includes the non-Markovian effects of the environmental affects, and it does not need the perturbation approximation in solving the dynamics of systems of interest. It implies that the coherence helps the EET between chromophores through lasting the transfer time rather than enhancing the transfer rate of the EET. In particular, the non-Markovian environment greatly increases the efficiency of the EET in the photosynthesis systems.
Attosecond dynamics of electron correlation in doubly excited atomic states
We have solved the time-dependent Schroedinger equation describing the simultaneous interaction of the He 1s2s 1S state with two laser-generated pulses of trapezoidal or Gaussian shape, of duration 86 fs and of frequencies ω1=1.453 au and ω2=1.781 au. The system is excited to the energy region of two strongly correlated doubly excited states, chosen for this study according to specific criteria. It is demonstrated quantitatively that, provided one focuses on the dynamics occurring within the attosecond timescale, the corresponding orbital configurations, 2s2p and 2p3d 1P0, exist as nonstationary states, with occupation probabilities that are oscillating as the states decay exponentially into the 1sεp continuum, during and after the laser-atom interaction. It follows that it is feasible to probe by attosecond pulses the motion of configurations of electrons as they correlate via the total Hamiltonian. For the particular system studied here, the probe pulses could register the oscillating doubly excited configurations by de-exciting to the He 1s3d 1D state, which emits at 6680 A. (author). Letter-to-the-editor
Excitation and dynamics of liquid tin micrometer droplet generation
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.
Stochastic resonance in discrete excitable dynamics on graphs
Highlights: ► We explore the propagation of excitations through a network under the influence of noise. ► Special emphasis is on the application to neuroscience. ► A novel labeling technique of signal excitations is introduced and compared to the classical signal-to-noise ratio. ► We show that noise can lead to an enhanced signal propagation, with a peak in the signal-to-noise ratio at intermediate noise intensities. - Abstract: How signals propagate through a network as a function of the network architecture and under the influence of noise is a fundamental question in a broad range of areas dealing with signal processing - from neuroscience to electrical engineering and communication technology. Here we use numerical simulations and a mean-field approach to analyze a minimal dynamic model for signal propagation. By labeling and tracking the excitations propagating from a single input node to remote output nodes in random networks, we show that noise (provided by spontaneous node excitations) can lead to an enhanced signal propagation, with a peak in the signal-to-noise ratio at intermediate noise intensities. This network analog of stochastic resonance is not captured by a mean-field description that incorporates topology only on the level of the average degree, indicating that the detailed network topology plays a significant role in signal propagation.
Dynamics of two-electron excitations in helium
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 (β), 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 σn, and photoelectron angular distributions βn were measured for all possible final ionic states He+(n) in the region of the double excitations N(K,T)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
Dynamics of two-electron excitations in helium
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.
Excited state dynamics of the astaxanthin radical cation
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.
Adaptive Dynamic Surface Control for Generator Excitation Control System
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.
Coherent and Incoherent Structural Dynamics in Laser-Excited Antimony
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.
Control of hair cell excitability by vestibular primary sensory neurons.
Brugeaud, Aurore; Travo, Cécile; Demêmes, Danielle; Lenoir, Marc; Llorens, Jordi; Puel, Jean-Luc; Chabbert, Christian
2007-01-01
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 of synapses was prevente...
Electronic excited states and relaxation dynamics in polymer heterojunction systems
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
Control of spiral-wave dynamics in active media by periodic modulation of excitability
Steinbock, Oliver; Zykov, Vladimir; Müller, Stefan C.
1993-12-01
EXCITABLE media exhibit a wide variety of geometrically complex spatio-temporal patterns, perhaps the most striking of which are rotating spiral waves. Spiral waves have now been observed in many excitable systems, including heart muscle1, aggregating slime-mould cells2, retinae3, CO oxidation on platinum4 and oscillatory chemical systems such as the Belousov-Zhabotinsky (BZ) reaction5,6. In the last case, the spiral cores trace out circular or hypocycloidal trajectories, depending on the specific reaction conditions7-9. In addition, if the excitability of the BZ reaction is light-sensitive10-13, constant illumination has been shown to influence the dynamics of spiral waves14,15. Here we investigate the effect of illumination that is periodically modulated in time. We find that, for a single set of reaction conditions, the motion of the spiral cores can be forced to describe a wide range of open and closed hypocycloidal trajectories, in phase with the applied modulation frequency. Numerical simulations using a modified version of the Oregonator model16,17 of the BZ reaction reproduce this behaviour. We suggest that the modulation of excitability with weak external forces might be used as a means for controlling the dynamics of other excitable media.
Sub-50 fs excited state dynamics of 6-chloroguanine upon deep ultraviolet excitation.
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
Dynamics of the excited state intramolecular charge transfer
The 6-dodecanoyl-2-dimethylaminonaphtalene (laurdan), a derivative of 6-propanoyl- 2-dimethylaminonaphthalene (prodan), has been used as a fluorescent probe in cell imaging, especially in visualizing the lipid rafts by the generalized polarization (GP) images, where GP=(I440-I490)/(I440+I490) with I being the fluorescence intensity. The fluorescence spectrum of laurdan is sensitive to its dipolar environment due to the intramolecular charge transfer (ICT) process in S1 state, which results in a dual emission from the locally excited (LE) and the ICT states. The ICT process and the solvation of the ICT state are very sensitive to the dipolar nature of the environment. In this work, the ICT of laurdan in ethanol has been studied by femtosecond time resolved fluorescence (TRF), especially TRF spectra measurement without the conventional spectral reconstruction method. TRF probes the excited states exclusively, a unique advantage over the pump/probe transient absorption technique, although time resolution of the TRF is generally lower than transient absorption and the TRF spectra measurement was possible only though the spectral reconstruction. Over the years, critical advances in TRF technique have been made in our group to achieve <50 fs time resolution with direct full spectra measurement capability. Detailed ICT and the subsequent solvation processes can be visualized unambiguously from the TRF spectra. Fig. 1 shows the TRF spectra of laurdan in ethanol at several time delays. Surprisingly, two bands at 433 and 476 nm are clearly visible in the TRF spectra of laurdan even at T = 0 fs. As time increases, the band at 476 nm shifts to the red while its intensity increases. The band at 433 nm also shifts slightly to the red, but loses intensity as time increases. The intensity of the 476 nm band reaches maximum at around 5 ps, where it is roughly twice as intense as that at 0 fs, and stays constant until lifetime decay is noticeable. The spectra were fit by two log
Excitation and Ionisation dynamics in high-frequency plasmas
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
Excitation Energy-Transfer Dynamics of Brown Algal Photosynthetic Antennas.
Kosumi, D; Kita, M; Fujii, R; Sugisaki, M; Oka, N; Takaesu, Y; Taira, T; Iha, M; Hashimoto, H
2012-09-20
Fucoxanthin-chlorophyll-a/c protein (FCP) complexes from brown algae Cladosiphon okamuranus TOKIDA (Okinawa Mozuku in Japanese) contain the only species of carbonyl carotenoid, fucoxanthin, which exhibits spectral characteristics attributed to an intramolecular charge-transfer (ICT) property that arises in polar environments due to the presence of the carbonyl group in its polyene backbone. Here, we investigated the role of the ICT property of fucoxanthin in ultrafast energy transfer to chlorophyll-a/c in brown algal photosynthesis using femtosecond pump-probe spectroscopic measurements. The observed excited-state dynamics show that the ICT character of fucoxanthin in FCP extends its absorption band to longer wavelengths and enhances its electronic interaction with chlorophyll-a molecules, leading to efficient energy transfer from fucoxanthin to chlorophyll-a. PMID:26295888
Investigations into photo-excited state dynamics in colloidal quantum dots
Singh, Gaurav
Colloidal Quantum dots (QDs) have garnered considerable scientific and technological interest as a promising material for next generation solar cells, photo-detectors, lasers, bright light-emitting diodes (LEDs), and reliable biomarkers. However, for practical realization of these applications, it is crucial to understand the complex photo-physics of QDs that are very sensitive to surface chemistry and chemical surroundings. Depending on the excitation density, QDs can support single or multiple excitations. The first part of this talk addresses evolution of QD excited state dynamics in the regime of low excitation intensity. We use temperature-resolved time-resolved fluorescence spectroscopy to study exciton dynamics from picoseconds to microseconds and use kinetic modeling based on classical electron transfer to show the effect of surface trap states on dynamics of ground-state exciton manifold in core-shell CdSe/CdS QDs. We show that the thickness of CdS shell plays an important role in interaction of CdSe core exciton states with nanocrystal environment, and find that a thicker shell can minimize the mixing of QD exciton states with surface trap states. I will then present an investigation into the dynamics of multiply-excited states in QDs. One of the key challenges in QD spectroscopy is to reliably distinguish multi- from single-excited states that have similar lifetime components and spectroscopic signatures. I will describe the development of a novel multi-pulse fluorescence technique to selectively probe multi-excited states in ensemble QD samples and determine the nature of the multi-excited state contributing to the total fluorescence even in the limit of low fluorescent yields. We find that in our sample of CdSe/CdS core/shell QDs the multi-excited emission is dominated by emissive trion states rather than biexcitons. Next, I will discuss the application of this technique to probe exciton-plasmon coupling in layered hybrid films of QD/gold nanoparticles
Deep Brain Stimulation: More Complex than the Inhibition of Cells and Excitation of Fibers.
Florence, Gerson; Sameshima, Koichi; Fonoff, Erich T; Hamani, Clement
2016-08-01
High-frequency deep brain stimulation (DBS) is an effective treatment for some movement disorders. Though mechanisms underlying DBS are still unclear, commonly accepted theories include a "functional inhibition" of neuronal cell bodies and the excitation of axonal projections near the electrodes. It is becoming clear, however, that the paradoxical dissociation "local inhibition" and "distant excitation" is far more complex than initially thought. Despite an initial increase in neuronal activity following stimulation, cells are often unable to maintain normal ionic concentrations, particularly those of sodium and potassium. Based on currently available evidence, we proposed an alternative hypothesis. Increased extracellular concentrations of potassium during DBS may change the dynamics of both cells and axons, contributing not only to the intermittent excitation and inhibition of these elements but also to interrupt abnormal pathological activity. In this article, we review mechanisms through which high extracellular potassium may mediate some of the effects of DBS. PMID:26150316
Oncotripsy: Targeting cancer cells selectively via resonant harmonic excitation
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.
Oncotripsy: Targeting cancer cells selectively via resonant harmonic excitation
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.
Ultrafast excited state dynamics in 9,9'-bifluorenylidene.
Conyard, Jamie; Heisler, Ismael A; Browne, Wesley R; Feringa, Ben L; Amirjalayer, Saeed; Buma, Wybren Jan; Woutersen, Sander; Meech, Stephen R
2014-08-01
9,9'-Bifluorenylidene has been proposed as an alternative and flexible electron acceptor in organic photovoltaic cells. Here we characterize its excited state properties and photokinetics, combining ultrafast fluorescence and transient IR measurements with quantum chemical calculations. The fluorescence decay is ultrafast (sub-100 fs) and remarkably independent of viscosity. This suggests that large scale structure change is not the primary relaxation mode. The ultrafast decay populates a dark state characterized by distinct vibrational and electronic spectra. This state decays with a 6 ps time constant to a hot ground state that ultimately populates the initial state with a 20 ps time constant; these times are also insensitive to solvent viscosity. No metastable intermediate structures are resolved in the photocycle after population of the dark state. The implications of these results for the operation of 9,9'-bifluorenylidene as an electron acceptor and as a potential molecular switch are discussed. PMID:25025227
Bruneau, B.; Diomede, P.; Economou, D. J.; Longo, S.; Gans, T.; O’Connell, D.; Greb, A.; Johnson, E.; Booth, J.-P.
2016-08-01
Parallel plate capacitively coupled plasmas in hydrogen at relatively high pressure (~1 Torr) are excited with tailored voltage waveforms containing up to five frequencies. Predictions of a hybrid model combining a particle-in-cell simulation with Monte Carlo collisions and a fluid model are compared to phase resolved optical emission spectroscopy measurements, yielding information on the dynamics of the excitation rate in these discharges. When the discharge is excited with amplitude asymmetric waveforms, the discharge becomes electrically asymmetric, with different ion energies at each of the two electrodes. Unexpectedly, large differences in the \\text{H}2+ fluxes to each of the two electrodes are caused by the different \\text{H}3+ energies. When the discharge is excited with slope asymmetric waveforms, only weak electrical asymmetry of the discharge is observed. In this case, electron power absorption due to fast sheath expansion at one electrode is balanced by electron power absorption at the opposite electrode due to a strong electric field reversal.
Effects of abnormal excitation on the dynamics of spiral waves
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).
Marks, M.; Sachs, S.; Schwalb, C. H.; Schöll, A.; Höfer, U.
2013-09-01
We present an investigation of the electronic structure and excited state dynamics of optically excited 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) thin films adsorbed on Ag(111) using two-photon photoemission spectroscopy (2PPE). 2PPE allows us to study both occupied and unoccupied electronic states, and we are able to identify signals from the highest occupied and the two lowest unoccupied electronic states of the PTCDA thin film in the 2PPE spectra. The energies for occupied states are identical to values from ultraviolet photoelectron spectroscopy. Compared to results from inverse photoelectron spectroscopy (IPES), the 2PPE signals from the two lowest unoccupied electronic states, LUMO and LUMO+1, are found at 0.8 eV and 1.0 eV lower energies, respectively. We attribute this deviation to the different final states probed in 2PPE and IPES and the attractive interaction of the photoexcited electron and the remaining hole. Furthermore, we present a time-resolved investigation of the excited state dynamics of the PTCDA film in the femtosecond time regime. We observe a significantly shorter inelastic excited state lifetime compared to findings from time-resolved photoluminescence spectroscopy of PTCDA single crystals which could originate from excitation quenching by the metal substrate.
Study of incomplete fusion dynamics: analysis of excitation functions
With a view to study complete fusion and incomplete fusion in several projectile target combinations, a programme of precise measurements of cross-sections and analysis of excitation functions has been undertaken. As a part of the ongoing programme, excitation functions for six reactions in 16O + 169Tm system have been measured
Akchurin, Garif G.; Seleverstov, George A.; Kamenskih, Tatyana G.; Akchurin, George G.; Bondarenko, Olga A.
2002-07-01
The nonlinear response of the Hodgkin-Huxley model neuron with external electrical pulsed was investigated. Dynamic response of somatic frog nerve on electrical pulsed duration was study in vitro. Transcutaneous millisecond of excitation of the ganglion cell of the human retina by electric uses is used for diagnosis, determination of the extent of optic nerve damage, and also partial restoration of visual function in patients with glaucoma, myopia and different types of optic nerve atrophy. Correlation between the threshold of phosphen formation and duration of the stimulating electric pulses was determined experimentally in normal eyes and in eyes with various pathologies. Comparison of optical and electrical scintillating frequency gives information about the dynamic processes in the normal and pathological retina.
Excitation-energy sorting in superfluid fission dynamics
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.
Excitation-energy sorting in superfluid fission dynamics
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. (authors)
The quantum dynamics problem for a 1D chain consisting of 2N + 1 sites (N ≫ 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 2 fragments and predicts the possibility of a nondissipative energy transfer between reaction centers associated with such chains.
Vrakking Marc J.J.
2013-03-01
Full Text Available We used velocity-map-imaging to measure electronic and nuclear dynamics in N2 molecules excited by a train of attosecond pulses. A time-to-space mapping of autoionization channel is demonstrated. It is found that the autoionization becomes energetically allowed when the two nuclei are still very close (~ 3 Å and that it can be coherently manipulated by a strong femtosecond infrared pulse.
Simultaneous live cell imaging using dual FRET sensors with a single excitation light.
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.
Bogner, Lea; Yang, Zechao; Corso, Martina; Fitzner, Roland; Bäuerle, Peter; Franke, Katharina J; Pascual, José Ignacio; Tegeder, Petra
2015-10-28
Dicyanovinyl (DCV)-substituted oligothiophenes are promising donor materials in vacuum-processed small-molecule organic solar cells. Here, we studied the structural and the electronic properties of DCV-dimethyl-pentathiophene (DCV5T-Me2) adsorbed on Au(111) from submonolayer to multilayer coverages. Using a multi-technique experimental approach (low-temperature scanning tunneling microscopy/spectroscopy (STM/STS), atomic force microscopy (AFM), and two-photon photoemission (2PPE) spectroscopy), we determined the energetic position of several affinity levels as well as ionization potentials originating from the lowest unoccupied molecular orbitals (LUMO) and the highest occupied molecular orbitals (HOMO), evidencing a transport gap of 1.4 eV. Proof of an excitonic state was found to be a spectroscopic feature located at 0.6 eV below the LUMO affinity level. With increasing coverage photoemission from excitonic states gains importance. We were able to track the dynamics of several electronically excited states of multilayers by means of femtosecond time-resolved 2PPE. We resolved an intriguing relaxation dynamics involving four processes, ranging from sub-picosecond (ps) to several hundred ps time spans. These show a tendency to increase with increasing coverage. The present study provides important parameters such as energetic positions of transport levels as well as lifetimes of electronically excited states, which are essential for designing organic-molecule-based optoelectronic devices. PMID:26414934
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.
Microbial Cell Dynamics Lab (MCDL)
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...
Molecular Dynamics Simulation of Chain Folding for Polyethylene Subjected to Vibration Excitation
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.
The Influence of Surface Plasmons on Excited State Dynamics in PTCDA
Azarova, N. A.
Organic thin film solar cells can be paired with nanostructured substrates to overcome the issue of narrow spectral absorption in a thin-film configuration. The nanostructured surface acts not only as an effective scattering back reflector to increase the light path within the absorbing thin film but also affords plasmonic activity. The interface between the metal and the absorbing chromophore supports surface plasmon modes. The associated strong electromagnetic field can potentially couple with excitations of the chromophore, altering its exciton dynamics. Such a plasmon-exciton coupling can lead to control over excitation processes, namely singlet fission. Singlet fission is a sharing of excited state energy between chromophores that may regulate instances of multi-exciton generation, allowing the solar cell efficiency to exceed the thermodynamical Shockley-Queisser limit. The current investigation focuses on hybridization of the plasmon and molecular exciton. We coat an organic semiconductor, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA), on the nanogratings consisting of lines of Ag on a substrate coated with a thick Ag backing. A dielectric spacer layer is included between the organic and the metal in some samples to eliminate any reaction between the two. The SP resonance of the grating is tuned through a PTCDA exciton line by sweeping the incident wave vector. Successful anticrossing between the plasmon and the exciton peaks would be observed in steady-state reflectance data as a function of angle. Though a detailed analysis of reflectance spectra has not been completed, the potential for plasmon-exciton hybdridization is demonstrated.
Ultrafast dynamics and excited state deactivation of [Ru(bpy)2Sq]+ (Ru-Sq)
Excited state dynamics of Ru-Sq has been studied using time resolved transient absorption spectroscopy with a time resolution of about 100fs. [Ru(bpy)2Sq]+, where bpy is the bipyridyl and Sq is the semi quinone is known to have two ground state absorption bands corresponding to two different metal to ligand charge transfer (MLCT) states. The absorption band centered on 460 nm is assigned to Ru(d) to bpy (π*) and the one on 890 nm is assigned to Ru(d) to Sq(π*). Significantly different excited state relaxation dynamics for both the MLCT states have been observed exciting both the bands separately. (author)
Elastic Dynamic Stability of Big-Span Power Transmission Tower Subjected to Seismic Excitations
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.
ANALYSIS OF GLOBAL DYNAMICS IN A PAIAMETIICALLY EXCITED THIN PLATE
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.
Ultrafast thermal dynamics of nano-ripples formation via laser double pulses excitation
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.
Time-resolved excitation dynamics in emeraldine base
Menšík, Miroslav; Rais, David; Pfleger, Jiří
Wroclaw: Institute of Physical and Theoretical Chemistry, Wroclaw University of Technology , 2014 - (Sobolewska, A.; Janus, K.). s. 36 [International Conference Electronic and Related Properties of Organic Solids /13./ - ERPOS 2014. 06.07.2014-10.07.2014, Świeradów Zdrój] R&D Projects: GA MŠk(CZ) LD14011; GA MŠk LH12186 Institutional support: RVO:61389013 Keywords : transient absorption spectroscopy * emeraldine base * excitation transfer Subject RIV: BM - Solid Matter Physics ; Magnetism
Ultrafast Structural Dynamics of Tertiary Amines upon Electronic Excitation
Cheng, Xinxin; Minitti, Michael P.; Deb, Sanghamitra; Zhang, Yao; Budarz, James; Weber, Peter M.
2011-06-01
The structural response of several tertiary amines to electronic excitation has been investigated using Rydberg Fingerprint Spectroscopy. The 3p Rydberg states are reached by excitation with a 5.93 eV photon while 3s states are populated by electronic relaxation from 3p state. We observe binding energy shifts on ultrafast time scales in all peaks that reflect the structural change of the molecular ion cores. The shifts are in the range of 15 meV to 30 meV, within time scales of less than 500 fs, depending on the specific molecular systems and the nature of the electronic state. In cases where the p states are spectrally separate, the trends of the energy shifts are different for the p_z and p_x_y Rydberg states whereas the p_z and s states are similar. This suggests that the response of the Rydberg states to structural displacements depends on the symmetry. Very fast binding energy shifts, observed on sub-picosecond time scales, are attributed to the structural adjustment from a pyramidal to a planar structure upon Rydberg excitation. The quantitative values of the binding energy shifts can also be affected by laser chirp, which we model using simulations.
Excited-State Dynamics of Carotenoids Studied by Femtosecond Transient Absorption Spectroscopy
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.
Excited state dynamics and isomerization in ruthenium sulfoxide complexes.
King, Albert W; Wang, Lei; Rack, Jeffrey J
2015-04-21
Molecular photochromic compounds are those that interconvert between two isomeric forms with light. The two isomeric forms display distinct electronic and molecular structures and must not be in equilibrium with one another. These light-activated molecular switch compounds have found wide application in areas of study ranging from chemical biology to materials science, where conversion from one isomeric form to another by light prompts a response in the environment (e.g., protein or polymeric material). Certain ruthenium and osmium polypyridine sulfoxide complexes are photochromic. The mode of action is a phototriggered isomerization of the sulfoxide from S- to O-bonded. The change in ligation drastically alters both the spectroscopic and electrochemical properties of the metal complex. Our laboratory has pioneered the preparation and study of these complexes. In particular, we have applied femtosecond pump-probe spectroscopy to reveal excited state details of the isomerization mechanism. The data from numerous complexes allowed us to predict that the isomerization was nonadiabatic in nature, defined as occurring from a S-bonded triplet excited state (primarily metal-to-ligand charge transfer in character) to an O-bonded singlet ground state potential energy surface. This prediction was corroborated by high-level density functional theory calculations. An intriguing aspect of this reactivity is the coupling of nuclear motion to the electronic wave function and how this coupling affects motions productive for isomerization. In an effort to learn more about this coupling, we designed a project to examine phototriggered isomerization in bis-sulfoxide complexes. The goal of these studies was to determine whether certain complexes could be designed in which a single photon excitation event would prompt two sulfoxide isomerizations. We employed chelating sulfoxides in this study and found that both the nature of the chelate ring and the R group on the sulfoxide affect
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.
The dynamics of N-methylpyrrole following excitation at wavelengths in the range 241.5-217.0 nm were studied using a combination of time-resolved photoelectron spectroscopy (TRPES), ab initio quantum dynamics calculations using the multi-layer multi-configurational time-dependent Hartree method, as well as high-level photoionization cross section calculations. Excitation at 241.5 and 236.2 nm results in population of the A2(πσ∗) state, in agreement with previous studies. Excitation at 217.0 nm prepares the previously neglected B1(π3py) Rydberg state, followed by prompt internal conversion to the A2(πσ∗) state. In contrast with the photoinduced dynamics of pyrrole, the lifetime of the wavepacket in the A2(πσ∗) state was found to vary with excitation wavelength, decreasing by one order of magnitude upon tuning from 241.5 nm to 236.2 nm and by more than three orders of magnitude when excited at 217.0 nm. The order of magnitude difference in lifetimes measured at the longer excitation wavelengths is attributed to vibrational excitation in the A2(πσ∗) state, facilitating wavepacket motion around the potential barrier in the N–CH3 dissociation coordinate
Dynamized Preparations in Cell Culture
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.
Exploring the vibrational fingerprint of the electronic excitation energy via molecular dynamics
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
Exploring the vibrational fingerprint of the electronic excitation energy via molecular dynamics
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.
Molecular excitation dynamics and relaxation quantum theory and spectroscopy
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
Detection of Damage in a Lattice Mast Excited by Wind by Dynamic Measurements
Pedersen, Lars; Brincker, Rune
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 response...... warning of a potential progress towards structural collapse prior to its occurrence....
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...
Dynamics of excitions created by a single picosecond pulse.
Paillotin, G; Swenberg, C E
A theoretical analysis of bimolecular annihilation in finite domains is presented. A Pauli master equation is formulated for the case of varying incident delta function excitation sources. Expressions for the quantum fluorescence yield and its time dependence are derived. The relationship between the fluorescence yield and the number of hits per domain depends on two parameters: the rate constant of bimolecular exciton annihilation and the dimension of the domain in which this annihilation occurs. Recent experimental results imply that the exciton diffusion constant (D) is large (D approximately to greater than 10(-3) cm2 S-1) and that the photosystem II domains may contain as many as five photosynthetic units. An analysis of the time decay of the fluorescence indicates that, for a few hits per domain, the decay may be considered as exponential but for many hits it becomes non-exponential. Thus the fluorescence decay depends on the intensity of the excitation source and/or on the dimension of the domains. Conditions which change the effective size of the domain may change the shape of the fluorescence decay. Some biological consequences and experimental applications of this theory are presented. PMID:256530
Structural Influence on Excited State Dynamics in Simple Amines
Klein, Liv Bærenholdt
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 is...... sensitive collection of photoelectron spectra. In particular, the angleresolved data available from the VMI approach provides highly detailed mechanistic insight about the relaxation pathways. One striking novel nding is that for tertiary amines, the critical factor driving the non-adiabatic dynamics is the...
Excitable human dynamics driven by extrinsic events in massive communities
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.
Yan Deng; Bin Zhou; Chao Xing; Rong Zhang
2014-01-01
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 rep...
Dynamic polarization potential for heavy-ion scattering induced by multiple Coulomb excitation
In heavy-ion reactions the strong electromagnetic interactions lead to Coulomb excitation effects which are superimposed on the nuclear and static-Coulomb forces. In elastic scattering these effects can be accounted for by a long-range dynamic 'Coulomb polarization potential'. For rather heavy ions, multiple Coulomb excitation becomes important. Here the authors report on a polarization potential which takes such multiple processes into account (at least in the semi-classical approximation). (orig./AH)
Dynamics of Vibration Machine with Air Flow Excitation and Restrictions on Phase Coordinates
Vība, J; Beresņevičs, V; Štāls, L; Eiduks, M; Kovals, E; Kruusmaa, M.
2010-01-01
The objective of presented article is to show possibilities of practical use of air or liquid flow in vibration engineering. Dynamics of vibration machine with constant air or liquid flow excitation is considered. In the first part vibration motion of the machine working head under constant air or liquid flow velocity excitation is investigated. The main idea is to find out optimal control law for variation of additional surface area of vibrating object within limits. The criterion of optimiz...
Ultrafast electronic dynamics in laser-excited crystalline bismuth
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
Excitation and recombination dynamics of vacancy-related spin centers in silicon carbide
We generate silicon vacancy related defects in high-quality epitaxial silicon carbide layers by means of electron irradiation. By controlling the irradiation fluence, the defect concentration is varied over several orders of magnitude. We establish the excitation profile for optical pumping of these defects and evaluate the optimum excitation wavelength of 770 nm. We also measure the photoluminescence dynamics at room temperature and find a monoexponential decay with a characteristic lifetime of 6.1 ns. The integrated photoluminescence intensity depends linear on the excitation power density up to 20 kW/cm2, indicating a relatively small absorption cross section of these defects
Excitation and recombination dynamics of vacancy-related spin centers in silicon carbide
Hain, T. C.; Hertel, T. [Institute of Physical and Theoretical Chemistry, Julius-Maximilian University of Würzburg, 97074 Würzburg (Germany); Fuchs, F.; Astakhov, G. V., E-mail: astakhov@physik.uni-wuerzburg.de [Experimental Physics VI, Julius-Maximilian University of Würzburg, 97074 Würzburg (Germany); Soltamov, V. A. [Ioffe Physical-Technical Institute, 194021 St. Petersburg (Russian Federation); Baranov, P. G. [Ioffe Physical-Technical Institute, 194021 St. Petersburg (Russian Federation); St. Petersburg State Polytechnical University, 195251 St. Petersburg (Russian Federation); Dyakonov, V., E-mail: dyakonov@physik.uni-wuerzburg.de [Experimental Physics VI, Julius-Maximilian University of Würzburg, 97074 Würzburg (Germany); Bavarian Center for Applied Energy Research (ZAE Bayern), 97074 Würzburg (Germany)
2014-04-07
We generate silicon vacancy related defects in high-quality epitaxial silicon carbide layers by means of electron irradiation. By controlling the irradiation fluence, the defect concentration is varied over several orders of magnitude. We establish the excitation profile for optical pumping of these defects and evaluate the optimum excitation wavelength of 770 nm. We also measure the photoluminescence dynamics at room temperature and find a monoexponential decay with a characteristic lifetime of 6.1 ns. The integrated photoluminescence intensity depends linear on the excitation power density up to 20 kW/cm{sup 2}, indicating a relatively small absorption cross section of these defects.
Beljonne, D; Hennebicq, E; Daniel, C; Herz, L M; Silva, C; Scholes, G D; Hoeben, F J M; Jonkheijm, P; Schenning, A P H J; Meskers, S C J; Phillips, R T; Friend, R H; Meijer, E W
2005-06-01
Atomistic models based on quantum-chemical calculations are combined with time-resolved spectroscopic investigations to explore the migration of electronic excitations along oligophenylenevinylene-based chiral stacks. It is found that the usual Pauli master equation (PME) approach relying on uncoherent transport between individual chromophores underestimates the excitation diffusion dynamics, monitored here by the time decay of the transient polarization anisotropy. A better agreement to experiment is achieved when accounting for excitation delocalization among acceptor molecules, as implemented in a modified version of the PME model. The same models are applied to study light harvesting and trapping in guest-host systems built from oligomers of different lengths. PMID:16852286
Different dynamics of ultraviolet upconversion in Tm3+:ZBLAN glass under blue laser excitation
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
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.
Tracking excited-state charge and spin dynamics in iron coordination complexes
Zhang, Wenkai; Alonso-Mori, Roberto; Bergmann, Uwe;
2014-01-01
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......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......,2'-bipyridine)(3)](2+), where the excited-state charge and spin dynamics involved in the transition from a low-to a high-spin state (spin crossover) have long been a source of interest and controversy(6-15). Here we demonstrate that femtosecond resolution X-ray fluorescence spectroscopy, with its sensitivity to...
Ultrafast dynamics in DNA base pairs following ultraviolet excitation.
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.
Possible dynamical limitations to excitation energy storage in nuclei
The dependence of the relative populations of particle unbound states on the associated charged particle multiplicity and on the total kinetic energy of the two decay products was investigated for 40Ar induced reactions on 197Au at E/A=60 MeV. The measurements indicate that the relative populations exhibit little sensitivity to the violence of the collision and to the time of emission. Implications of these results upon the dynamics of the reaction are discussed
Lattice dynamics and methyl rotational excitations of 2-butyne
Kirstein, O.; Prager, M.; Johnson, M. R.; Parker, S. F.
2002-01-01
On the basis of the recently determined low temperature crystal structure the lattice dynamics of 2-butyne and a single particle methyl rotational potential are calculated using pair potential parameters given by Williams in 1974 within the model of semirigid molecules. In the regime of lattice modes the existence of four methyl librational bands with significant dispersion can explain the measured density of states. The single particle librational energy obtained for the rotational potential...
Excited carrier dynamics and transport in plasmonic nanostructures
Sundararaman, Ravishankar; Narang, Prineha; Jermyn, Adam; Atwater, Harry; Goddard, William, III
Surface plasmon resonances provide a pathway to efficiently capture electromagnetic radiation in sub-wavelength structures for energy conversion and photodetection at the nano scale. The complete mechanism involves several microscopic steps spanning length scales from atomic dimensions to tens or hundreds of nanometers, posing challenges for experimental characterization and for first-principles predictions. To provide the basis for predicting and optimizing the complex interplay of materials and geometric effects in plasmon decay-induced excited carrier phenomena, we combined ab initio electronic structure calculations, electromagnetic simulations and Boltzmann transport models. In Au, Ag, Cu and Al nanostructures, we find that initial carrier distributions as well as their subsequent transport, relaxation and thermalization are sensitive to electronic structure, exhibiting strong asymmetries between electrons and holes. We predict energy-dependent spatially-resolved carrier distributions collected in plasmonic nanostructures with strong field inhomogeneities, and explore the possibility of tailoring materials and geometry to collect the carrier distributions needed for such applications as photochemically driven CO2 reduction and water splitting. This material is based upon work performed by JCAP, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993.
Fluorescent and dynamic properties of optically excited dysprosium trifluoride
Xu, Li-Wen; Crosswhite, H. M.; Hessler, Jan P.
1984-07-01
Fluorescent, excitation, and absorption spectra of DyF3 are reported. The energies of the electronic states of the ground level are significantly shifted compared to those of the dilute system DyxLa1-xF3 and are consistent with recent specific heat measurements from 5 to 350 K. The fluorescent decay rate K of the (4F9/2)1 state follows the equation K(μs-1)=1.600+0.0307 T(K), where T(K) is the absolute temperature. At 0 K the quantum efficiency is approximately 4.5×10-4. The decay rate is determined by the donor-to-acceptor transfer rate, where an acceptor is a pair of coupled dysprosium ions which deactivate the (4F9/2)1 state. Cross relaxation of the form 4F9/2+6H15/2→6F3/2+6H5/2 is calculated to be the dominant dipole-dipole decay channel. Comparison of high-resolution absorption line shapes, measured above 4.2 K, and below the ferromagnetic transition 2.53 K shows a shift of the line centers, and a reduction, by a factor of 6 in the linewidths. These results are consistent with analogous measurements performed on the Ising antiferromagnet dysprosium aluminum garnet and reflect the short-range order of the system.
Dynamic Response Analysis for Embedded Large-Cylinder Breakwaters Under Wave Excitation
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.
Dynamized Preparations in Cell Culture
Girija Kuttan; Korengath Chandran Preethi; Ramadasan Kuttan; Ellanzhiyil Surendran Sunila
2009-01-01
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 ...
Numerical computation of dynamically important excited states of many-body systems
Łącki, Mateusz; Delande, Dominique; Zakrzewski, Jakub
2012-07-01
We present an extension of the time-dependent density matrix renormalization group, also known as the time evolving block decimation algorithm, allowing for the computation of dynamically important excited states of one-dimensional many-body systems. We show its practical use for analyzing the dynamical properties and excitations of the Bose-Hubbard model describing ultracold atoms loaded in an optical lattice from a Bose-Einstein condensate. This allows for a deeper understanding of nonadiabaticity in experimental realizations of insulating phases.
Dynamical Coupling of Pygmy and Giant Resonances in Relativistic Coulomb Excitation
Brady, N; Bertulani, C A; Thomas, J
2016-01-01
We study the Coulomb excitation of pygmy dipole resonances (PDR) in heavy ion reactions at 100 MeV/nucleon and above. The reactions 68Ni+197Au and 68Ni+208Pb are taken as a practical examples. Our goal is to address the question of the influence of giant resonances on the PDR as the dynamics of the collision evolves. We show that the coupling to the giant resonances affects considerably the excitation probabilities of the PDR, a result that indicates the need of an improved theoretical treatment of the reaction dynamics at these bombarding energies.
Excitation dynamics of micro-structured atmospheric pressure plasma arrays
Boettner, H; Waskoenig, J.; Connell, D O '; Winter, J; Schulz-von der Gathen, V
2010-01-01
Abstract The spatial dynamics of the optical emission from an array of 50 times 50 individual micro cavity plasma devices are investigated. The array is operated in argon and argon-neon mixtures close to atmospheric pressure with an AC voltage. The optical emission is analysed with phase and space resolution. It has been found that the emission is not continuous over the entire AC period, but occurs once per half period. Each of the observed emission phases shows a self-pulsing of the disc...
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
Nonlinear dynamics of a sliding beam on two supports under sinusoidal excitation
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.
Dynamical effects in fission investigated at high excitation energy
Benlliure J.
2016-01-01
Full Text Available The experimental techniques used for the investigation of nuclear fission have progressed considerably during the last decade. Most of this progress is based on the use of the inverse kinematics technique allowing for the first time the complete isotopic and kinematic characterization of both fission fragments. These measurements make possible to characterize the fissioning system at saddle and at scission, and can be used to benchmark fission model calculations. One of the important ingredients in transport models describing the dynamics of the process is the dissipation parameter, governing the coupling between intrinsic and collective degrees of freedom. Recent experiments got access to the magnitude of this parameter and could also investigate its dependence in temperature and deformation.
Dynamical effects in fission investigated at high excitation energy
Benlliure, J.
2016-05-01
The experimental techniques used for the investigation of nuclear fission have progressed considerably during the last decade. Most of this progress is based on the use of the inverse kinematics technique allowing for the first time the complete isotopic and kinematic characterization of both fission fragments. These measurements make possible to characterize the fissioning system at saddle and at scission, and can be used to benchmark fission model calculations. One of the important ingredients in transport models describing the dynamics of the process is the dissipation parameter, governing the coupling between intrinsic and collective degrees of freedom. Recent experiments got access to the magnitude of this parameter and could also investigate its dependence in temperature and deformation.
Two-photon excitation in living cells induced by low-power cw laser beams
Koenig, Karsten; Krasieva, Tatiana B.; Liu, Yagang; Berns, Michael W.; Tromberg, Bruce J.
1996-05-01
We demonstrate multi-photon excitation in optically-trapped living cells. Intracellular non- resonant two-photon excitation of endogenous and exogenous chromophores was induced by CW near infrared (NIR) trapping beams of 105 mW power. In the case of fluorescent chromophores, detection of NIR-excited visible fluorescence was achieved by imaging and spectroscopy methods. Trap-induced, two-photon excited fluorescence was employed as a novel diagnostic method to monitor intracellular redox state and cell vitality of single motile spermatozoa and Chinese hamster ovary cells. We found, that nonlinear absorption of NIR photons NIR, single-frequency traps (`optical tweezers') for micromanipulation of vital cells.
Mapping Ultrafast Dynamics of Highly Excited H2by Attosecond VUV-Radiation
Weber, Thorsten; Sturm, Felix; Wright, Travis; Ray, Dipanwita; Shivaram, Niranjan; Slaughter, Daniel; Bocharova, Irina; Ranitovic, Predrag; Belkacem, Ali
2016-05-01
We show how attosecond vacuum ultraviolet (VUV) and femtosecond infrared (IR) radiation can be used to excite and map dynamics of a highly excited neutral hydrogen molecule. By using time-delayed, strong laser pulses and ion imaging, we map the dynamics of highly-excited, bound states of hydrogen molecules. Due to the large stretching amplitude of the B electronic state, excited by the 9th harmonic of the fundamental laser frequency, the effective ionization potential of the hydrogen molecular ion changes substantially as the nuclear wave packet (NWP) vibrates in the bound, B potential energy curve. Therefore, the probability of ionizing the neutrally-excited hydrogen molecule by the IR probe pulse changes as the NWP evolves in the B potential. We probe this dynamics by ionizing the vibrating molecule by means of time-delayed IR radiation, and identify the dissociation channels with 3D-momentum ion imaging. Supported by DOE under Contract No. DE-AC02-05CH11231.
Parra-Rivas, P; Gomila, D; Matías, M A; Colet, P; Gelens, L
2016-01-01
We have reported in Phys. Rev. Lett. 110, 064103 (2013)PRLTAO0031-900710.1103/PhysRevLett.110.064103 that in systems which otherwise do not show oscillatory dynamics, the interplay between pinning to a defect and pulling by drift allows the system to exhibit excitability and oscillations. Here we build on this work and present a detailed bifurcation analysis of the various dynamical instabilities that result from the competition between a pulling force generated by the drift and a pinning of the solitons to spatial defects. We show that oscillatory and excitable dynamics of dissipative solitons find their origin in multiple codimension-2 bifurcation points. Moreover, we demonstrate that the mechanisms leading to these dynamical regimes are generic for any system admitting dissipative solitons. PMID:26871077
Collective excitations in liquid CD4: Neutron scattering and molecular-dynamics simulations
Guarini, E.; Bafile, U.; Barocchi, F.; Demmel, F.; Formisano, F.; Sampoli, M.; Venturi, G.
2005-12-01
We have investigated the dynamic structure factor S(Q,ω) of liquid CD4 at T = 97.7 K in the wave vector range 2 <= Q/nm-1 <= 15 by means of neutron scattering and molecular-dynamics simulation, in order to study the centre-of-mass collective dynamics. The agreement between the experimental spectra and those simulated using a recent ab initio based intermolecular potential is good, particularly at low Q. Underdamped collective excitations, detected in the whole experimental Q-range, characterize the dynamics of liquid CD4 as markedly different from that of other molecular liquids. Also, the energy and damping of collective excitations in methane are shown to differ considerably, even at the lowest measured Q-values, from those of linearized hydrodynamic modes. An empirical relation, able to reconcile the different wave vector ranges of mode propagation observed in disparate liquids, is investigated.
Markers of pathological excitability derived from principal dynamic modes of hippocampal neurons
Kang, Eunji E.; Zalay, Osbert C.; Serletis, Demitre; Carlen, Peter L.; Bardakjian, Berj L.
2012-10-01
Transformation of principal dynamic modes (PDMs) under epileptogenic conditions was investigated by computing the Volterra kernels in a rodent epilepsy model derived from a mouse whole hippocampal preparation, where epileptogenesis was induced by altering the concentrations of Mg2 + and K+ of the perfusate for different levels of excitability. Both integrating and differentiating PDMs were present in the neuronal dynamics, and both of them increased in absolute magnitude for increased excitability levels. However, the integrating PDMs dominated at all levels of excitability in terms of their relative contributions to the overall response, whereas the dominant frequency responses of the differentiating PDMs were shifted to higher ranges under epileptogenic conditions, from ripple activities (75-200 Hz) to fast ripple activities (200-500 Hz).
Self-modulated dynamics of a relativistic charged particle beam in plasma wake field excitation
Akhter, T.; Fedele, R.; Nicola, S. De; Tanjia, F.; Jovanović, D.; Mannan, A.
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.
Detection of Damage in a Lattice Mast Excited by Wind by Dynamic Measurements
Pedersen, Lars; Brincker, Rune
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 m...
Self modulated dynamics of a relativistic charged particle beam in plasma wake field excitation
Akhter, T; De Nicola, S; Tanjia, F; Jovanovic, D; Mannan, A
2015-01-01
Self modulated dynamics of a relativistic charged particle beam is reviewed 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.
Nonlinear dynamics of a support-excited flexible rotor with hydrodynamic journal bearings.
Dakel, M. Zaki; Baguet, Sébastien; Dufour, Régis
2014-01-01
The major purpose of this study is to predict the dynamic behavior of an on-board rotor mounted on hydrodynamic journal bearings in the presence of rigid support movements, the target application being turbochargers of vehicles or rotating machines subject to seismic excitation. The proposed on-board rotor model is based on Timoshenko beam finite elements. The dynamic modeling takes into account the geometric asymmetry of shaft and/or rigid disk as well as the six deterministic translations a...
Effect of carotenoid structure on excited-state dynamics of carbonyl carotenoids
Chábera, P.; Fuciman, M.; Hříbek, P.; Polívka, Tomáš
2009-01-01
Roč. 11, - (2009), s. 8795-8703. ISSN 1463-9076 R&D Projects: GA AV ČR IAA608170604 Institutional research plan: CEZ:AV0Z50510513 Keywords : excited-state dynamics * carbonyl carotenoids * femtosecond spectroscopy Subject RIV: BO - Biophysics Impact factor: 4.116, year: 2009
Fermionic Molecular Dynamics Multifragmentation in heavy-ion collisions and in excited nuclei
Feldmeier, H
1997-01-01
Within Fermionic Molecular Dynamics we investigate fragmentation of a compound system which was created in a heavy-ion collision at a beam energy in the Fermi energy domain and the decay of excited iron nuclei. We show that in FMD many-body correlations play an important role in the formation of fragments.
Turchinovich, Dmitry; Monozon, B. S.; Jepsen, Peter Uhd
2006-01-01
In this work we describe the ultrafast excitation kinetics of biased quantum well, arising from the optically induced dynamical screening of a bias electric field. The initial bia electric field inside the quantum well is screened by the optically excited polarized electron-hole pairs. This leads...... to a dynamical modification of the properties of the system within an excitation pulse duration. We calculate the excitation kinetics of a biased quantum well and the dependency of resulting electronic and optical properties on the excitation pulse fluence, quantum well width,and initial bias field...
The electrical behaviour of an excitable cell at different conditions
The Hodgkin-Huxley, H-H, model has been modified, in this work, to study the electrical behaviour of an excitable cell due to changes in the permeability of K and Na ions (gk and gNa), the simultaneous stochastic variations of gk and gNa, the current stimulus (Jstim) and the non-inactivation of Na-channel (NI - NaC). The amplitude and duration of the generated action potential (AP) was found to increase as gk increases, with the appearance of repetitive AP spikes in the range of 21.5 ≥ gk ≥ 3.5 while the K- and Na-currents (Jk and JNa) showed a pronounced decrease. On the other hand, the increase of gNa was accompanied by an increase in AP amplitudes and durations and also in Jk and JNa with the appearance of a repetitive AP at 1400 ≥ gNa ≥ 189 ms/cm2 whose frequency increases with the increase of gNa. Moreover, the stochastic variations in gk and gNa could generate a repetitive AP whose frequency could be changed either by changing the values of gk or gNa or both, and may represent an information carried by the sensory cells for example. The electrical behaviour of the simulated cell can also be affected by Jstim at different values of gk except at the range of 21.5 ≥ gk ≥ 3.5 ms/cm2 and also depended on NI - NaC fraction. (author). 11 refs, 9 figs, 4 tabs
Gonadal Steroids: Effects on Excitability of Hippocampal Pyramidal Cells
Teyler, Timothy J.; Vardaris, Richard M.; Lewis, Deborah; Rawitch, Allen B.
1980-08-01
Electrophysiological field potentials from hippocampal slices of rat brain show sex-linked differences in response to 1 × 10-10M concentrations of estradiol and testosterone added to the incubation medium. Slices from male rats show increased excitability to estradiol and not to testosterone. Slices from female rats are not affected by estradiol, but slices from female rats in diestrus show increased excitability in response to testosterone whereas slices from females in proestrus show decreased excitability.
Synchronization enhancement via an oscillatory bath in a network of self-excited cells
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.
Sieber-Blum, Maya
2011-01-01
Wong and Reiter have explored the possibility that hair follicle stem cells can give rise to basal cell carcinoma (BCC). They expressed in mice an inducible human BCC-derived oncogenic allele of Smoothened, SmoM2, under the control of either the cytokeratin 14 (K14) or cytokeratin 15 (K15) promoter. Smoothened encodes a G-protein-coupled receptor protein in the hedgehog pathway, the misregulation of which is implicated in BCC and other human cancers. Chronic injury is thought to be a contribu...
Fully Suspended, Five-Axis, Three-Magnetic-Bearing Dynamic Spin Rig With Forced Excitation
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.
Correlated electron-ion dynamics: the excitation of atomic motion by energetic electrons
Correlated electron-ion dynamics (CEID) is an extension of molecular dynamics that allows us to introduce in a correct manner the exchange of energy between electrons and ions. The formalism is based on a systematic approximation: small amplitude moment expansion. This formalism is extended here to include the explicit quantum spread of the ions and a generalization of the Hartree-Fock approximation for incoherent sums of Slater determinants. We demonstrate that the resultant dynamical equations reproduce analytically the selection rules for inelastic electron-phonon scattering from perturbation theory, which control the mutually driven excitations of the two interacting subsystems. We then use CEID to make direct numerical simulations of inelastic current-voltage spectroscopy in atomic wires, and to exhibit the crossover from ionic cooling to heating as a function of the relative degree of excitation of the electronic and ionic subsystems
Dynamic near-field nanofocusing by V-shaped metal groove via a femtosecond laser excitation
Du, Guangqing; Yang, Qing; Chen, Feng; Lu, Yu; Ou, Yan; Yong, Jiale; Hou, Xun
2016-03-01
The ultrafast dynamics of plasmonic near-field nanofocusing by a V-shaped groove milled on Au film via a femtosecond laser excitation is theoretically studied based on finite element method. The spatiotemporal evolution of the focused e-fields around the V-groove geometry is obtained. It is revealed that the strong nanofocusing at the V-shaped groove occurs at the moderate electron temperature of 3000 K in the electron-phonon uncoupled state via a femtosecond laser pulse excitation. The phenomenon is explained as the electron thermal dynamics manipulation of plasmon resonances due to femtosecond laser fluence modifications. This study provides basic understanding of ultrafast dynamics of near-field nanofocusing in V-shaped geometry for wide applications in the fields such as super-resolution imaging, SERS, and photothermal therapy.
Exciton Dynamics in Photosynthetic Complexes: Excitation by Coherent and Incoherent Light
Mancal, Tomas
2010-01-01
In this paper we consider dynamics of a molecular system subjected to external pumping by a light source. Within a completely quantum mechanical treatment, we derive a general formula, which enables to asses effects of different light properties on the photo-induced dynamics of a molecular system. We show that once the properties of light are known in terms of certain two-point correlation function, the only information needed to reconstruct the system dynamics is the reduced evolution superoperator. The later quantity is in principle accessible through ultrafast non-linear spectroscopy. Considering a direct excitation of a small molecular antenna by incoherent light we find that excitation of coherences is possible due to overlap of homogeneous line shapes associated with different excitonic states. In Markov and secular approximations, the amount of coherence is significant only under fast relaxation, and both the populations and coherences between exciton states become static at long time. We also study th...
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 dynamics of eNOS-oxy with L-arginine substrate mainly occurs at the local site of heme, including ultrafast internal conversion within 400fs, vibrational cooling, charge transfer, and complete ground-state recovery within 1.4ps. 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. PMID:27183248
Estimate of dynamic stiffness and damping by forced excitation test of foundation on bedrock. Pt. 2
Based on the results of forced excitation tests of foundations on bedrock, dynamic complex stiffness (dynamic stiffness and damping) were obtained at many nuclear power plant sites. Experimental results were investigated by three-dimensional wave propagation theory considering layered stratum of bedrock. It is shown dynamic stiffness can be estimated with sufficient accuracy by considering layered stratum of bedrock. Also it is shown that by two-layered ground model estimate of damping characteristics is possible for foundations on multi-layered bedrock. (orig./HP)
Nonlinear excitation kinetics of biased quantum wells. Coherent dynamical screening effect
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 of the...... bandstructure of the quantum well, which is totally coherent with the temporal intensity distribution of the excitation laser pulse. We developed a time-resolved theoretical model of coherent dynamical screening, which predicts interesting fundamental consequences, such as nonlinear absorption and ultra...
Carbon nanorings with inserted acenes: breaking symmetry in excited state dynamics.
Franklin-Mergarejo, R; Alvarez, D Ondarse; Tretiak, S; Fernandez-Alberti, S
2016-01-01
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. PMID:27507429
Excited State Structural Dynamics of Carotenoids and ChargeTransfer Systems
Van Tassle, Aaron Justin
2006-09-01
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.
Carbon nanorings with inserted acenes: breaking symmetry in excited state dynamics
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.
Bement, William M; Leda, Marcin; Moe, Alison M; Kita, Angela M; Larson, Matthew E; Golding, Adriana E; Pfeuti, Courtney; Su, Kuan-Chung; Miller, Ann L; Goryachev, Andrew B; von Dassow, George
2015-11-01
Animal cell cytokinesis results from patterned activation of the small GTPase Rho, which directs assembly of actomyosin in the equatorial cortex. Cytokinesis is restricted to a portion of the cell cycle following anaphase onset in which the cortex is responsive to signals from the spindle. We show that shortly after anaphase onset oocytes and embryonic cells of frogs and echinoderms exhibit cortical waves of Rho activity and F-actin polymerization. The waves are modulated by cyclin-dependent kinase 1 (Cdk1) activity and require the Rho GEF (guanine nucleotide exchange factor), Ect2. Surprisingly, during wave propagation, although Rho activity elicits F-actin assembly, F-actin subsequently inactivates Rho. Experimental and modelling results show that waves represent excitable dynamics of a reaction-diffusion system with Rho as the activator and F-actin the inhibitor. We propose that cortical excitability explains fundamental features of cytokinesis including its cell cycle regulation. PMID:26479320
Excited state coherent dynamics in light-harvesting complexes from photosynthetic marine algae
Richards, G. H.; Wilk, K. E.; Curmi, P. M. G.; Quiney, H. M.; Davis, J. A.
2012-08-01
We explore coherence dynamics in light-harvesting complexes and their interactions with other electronic states and vibrational modes. This is achieved by utilizing a two-colour four-wave mixing spectroscopy to excite and analyse a specific coherence pathway in the phycocyanin-645 (PC645) light-harvesting complex. We observe the dephasing rate increase as a function of temperature and oscillations in the signal intensity as a function of waiting time which reveals coherent excitation of pathways not directly resonant with the laser pulses. This coherent excitation of non-resonant electronic states implies strong coupling to phonon modes, which is necessary if coherent energy transfer between non-resonant states is to play any role in photosynthetic energy transfer.
Excited state coherent dynamics in light-harvesting complexes from photosynthetic marine algae
We explore coherence dynamics in light-harvesting complexes and their interactions with other electronic states and vibrational modes. This is achieved by utilizing a two-colour four-wave mixing spectroscopy to excite and analyse a specific coherence pathway in the phycocyanin-645 (PC645) light-harvesting complex. We observe the dephasing rate increase as a function of temperature and oscillations in the signal intensity as a function of waiting time which reveals coherent excitation of pathways not directly resonant with the laser pulses. This coherent excitation of non-resonant electronic states implies strong coupling to phonon modes, which is necessary if coherent energy transfer between non-resonant states is to play any role in photosynthetic energy transfer. (paper)
On the Dynamics of Xylene Isomers Excited in the Vacuum-Ultraviolet (VUV) Region.
Papadopoulou, Christina C; Kaziannis, Spiridon; Kosmidis, Constantine
2016-08-01
We report on the dynamics of electronically excited o-, m-, and p-xylene on the femtosecond timescale by employing the vacuum-ultraviolet pump-IR probe mass spectrometry technique. The molecules were excited by the fifth harmonic (λ=160 nm) of a Ti:sapphire laser at a superposition of the S3 valence with several Rydberg states. The relaxation pathways were investigated by studying the parent P(+) and the fragment [P-H](+) and [P-CH3 ](+) time-resolved signals generated after interaction with the fundamental beam (λ=800 nm). Relaxation from the excited valence states was found to depend on the relative positions of the methyl groups on the ring. An increasing trend in the order omotion takes place. PMID:27128655
Bryk, Taras; Wax, J.-F.
2016-05-01
Using a combination of ab initio molecular dynamics and several fit models for dynamic structure of liquid metals, we explore an issue of possible manifestation of non-acoustic collective excitations in longitudinal dynamics having liquid Na as a case study. A model with two damped harmonic oscillators (DHOs) in time domain is used for analysis of the density-density time correlation functions. Another similar model with two propagating contributions and three lowest exact sum rules is considered, as well as an extended hydrodynamic model known as thermo-viscoelastic one which permits two types of propagating modes outside the hydrodynamic region to be used for comparison with ab initio obtained time correlation functions and calculations of dispersions of collective excitations. Our results do not support recent suggestions that, even in simple liquid metals, non-hydrodynamics transverse excitations contribute to the longitudinal collective dynamics and can be detected as a DHO-like spectral shape at their transverse frequency. We found that the thermo-viscoelastic dynamic model permits perfect description of the density-density and current-current time correlation functions of the liquid Na in a wide range of wave numbers, which implies that the origin of the non-hydrodynamic collective excitations contributing to longitudinal dynamics can be short-wavelength heat waves.
Photoluminescence and excited states dynamics in PbWO{sub 4}:Pr{sup 3+} crystals
Auffray, E. [CERN, Geneva 23, Geneva (Switzerland); Korjik, M. [Institute for Nuclear Problems, 11 Bobruiskaya, 220020 Minsk (Belarus); Shalapska, T. [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu (Estonia); Zazubovich, S., E-mail: svet@fi.tartu.ee [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu (Estonia)
2014-10-15
Luminescence and photo-thermally stimulated defects creation processes are studied for a Pr{sup 3+}-doped PbWO{sub 4} crystal at 4.2–400 K under excitation in the band-to-band, exciton, and charge-transfer transitions regions, as well as in the Pr{sup 3+}-related absorption bands. Emission spectra of Pr{sup 3+} centers depend on the excitation energy, indicating the presence of Pr{sup 3+} centers of two types. The origin of these centers is discussed. The 2.03–2.06 eV emission, arising from the {sup 1}D{sub 2}→{sup 3}H{sub 4} transitions of Pr{sup 3+} ions, is found to be effectively excited in a broad intense absorption band peaking at 4.2 K at 3.92 eV. By analogy with some other Pr{sup 3+}-doped compounds, this band is suggested to arise from an electron transfer from an impurity Pr{sup 3+} ion to the crystal lattice W{sup 6+} or Pb{sup 2+} ions. The dynamics of the Pr{sup 3+}-related excited states is clarified. In the PbWO{sub 4}:Pr crystal studied, the concentration of single oxygen and lead vacancies as traps for electrons and holes is found to be negligible. - Highlights: • Luminescence and defects creation processes in PbWO{sub 4}:Pr single crystal investigated. • Existence of Pr{sup 3+}-related luminescence centers of two types revealed. • Charge transfer origin of the intense 3.92 eV absorption/excitation band suggested. • Dynamics of the Pr{sup 3+}-related excited states clarified. • Negligible concentration of single oxygen and lead vacancies in PbWO{sub 4}:Pr concluded.
Combining spiral and target wave detection to analyze excitable media dynamics
Geberth, Daniel; Hütt, Marc-Thorsten
2010-01-01
Excitable media dynamics is the lossless active transmission of waves of excitation over a field of coupled elements, such as electrical excitation in heart tissue or nerve fibers, cAMP signaling in the slime mold Dictyostelium discoideum or waves of chemical activity in the Belousov-Zhabotinsky reaction. All these systems follow essentially the same generic dynamics, including undamped wave transmission and the self-organized emergence of circular target and self-sustaining spiral waves. We combine spiral recognition, using the established phase singularity technique, and a novel three-dimensional fitting algorithm for noise-resistant target wave recognition to extract all important events responsible for the layout of the asymptotic large-scale pattern. Space-time plots of these combined events reveal signatures of events leading to spiral formation, illuminating the microscopic mechanisms at work. This strategy can be applied to arbitrary excitable media data from either models or experiments, giving insight into for example the microscopic causes for formation of pathological spiral waves in heart tissue, which could lead to novel techniques for diagnosis, risk evaluation and treatment.
Dynamic quenching as a simple test for the mechanism of excited-state reaction
We report on comparative studies of dynamic fluorescence quenching of 3-hydroxyflavone (3HF) and of its novel analogs by nitric oxide spin compound TEMPO. These dyes exhibit the excited-state intramolecular proton transfer (ESIPT) reaction that allows observation of two separate bands in fluorescence emission - of initially excited form and of the product of ESIPT reaction. In the frame of two-state excited-state reaction formalism, we develop the theory predicting different dependence of intensities at two bands in steady-state spectra in the cases of thermodynamic and kinetic control of ESIPT. In line with these predictions, the quenching changes strongly the distribution of intensities between these bands for 3HF but does not change it for the novel compounds whose excited states exhibit strong charge transfer character. Based on these findings, we suggest that the quenching of fluorescence by an efficient collisional quencher can be a simple and convenient method using only the steady-state experiment for distinguishing the excited-state reactions occurring under thermodynamic or under kinetic controls. This method can be used for large-scale screening of a series of compounds - potential candidates for application in fluorescence sensor and biosensor technologies
Qiaoyun YAN; Hu DING; Liqun CHEN
2015-01-01
This investigation focuses on the nonlinear dynamic behaviors in the trans-verse vibration of an axially accelerating viscoelastic Timoshenko beam with the external harmonic excitation. The parametric excitation is caused by the harmonic fluctuations of the axial moving speed. An integro-partial-differential equation governing the transverse vibration of the Timoshenko beam is established. Many factors are considered, such as viscoelasticity, the finite axial support rigidity, and the longitudinally varying tension due to the axial acceleration. With the Galerkin truncation method, a set of nonlinear ordinary differential equations are derived by discretizing the governing equation. Based on the numerical solutions, the bifurcation diagrams are presented to study the effect of the external transverse excitation. Moreover, the frequencies of the two excitations are assumed to be multiple. Further, five different tools, including the time history, the Poincar´e map, and the sensitivity to initial conditions, are used to identify the motion form of the nonlinear vibration. Numerical results also show the characteristics of the quasiperiodic motion of the translating Timoshenko beam under an incommensurable re-lationship between the dual-frequency excitations.
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.
Excited-state dynamics in light-harvesting complex of Rhodobacter sphaeroides
LIU KangJun; LIU WeiMin; YAN YongLi; DONG ZhiWei; XU ChunHe; QIAN ShiXiong
2008-01-01
Photodynamics of peripheral antenna complexes, light-harvesting complex (LH2) of Rhodobacter (Rb) Sphaeroides 601, was studied using femtosecond pump-probe technique at different laser wavelengths. The obtained results reveal dramatic dynamical evolutions within B800 and B850 absorption bands of antenna complexes LH2. At excitation wavelength around 835 nm, a sharp photobleaching signal was observed which was assigned to the contribution of the two-exciton state, which was further confirmed by the power dependence measurement. Rate equations with eight-level scheme were used to calculate the population evolution in LH2 and the transient dynamics under femtosecond pulse excitation. The research results prove that not only the transition from ground state to one-exciton state but also that from one-exciton state to two-exciton state contribute to the photodynamics of B850.
Hutter, Marco; Fankhauser, Péter; Gehring, Christian; Bloesch, Michael; Hoepflinger, Mark A.; Siegwart, Roland
2014-01-01
This paper describes a hierarchical operational space control (OSC) method based on least square optimization and outlines different ways to reduce the dimensionality of the optimization vector. The framework allows to emulate various behaviors by prioritized task-space motion, joint torque, and contact force optimization. Moreover, a methodology is introduced to partially excite the natural dynamics of the robot by open-loop motor regulation while the entire behavior is stabilized by hierarc...
Shihab, Sylvain
2015-01-01
Development of impulsional laser enhanced the study of the magnetization dynamic in the temporal domain (fs-ns) with optical techniques. In thin ferromagnetic films with a weak optical absorption, excitation and optical mechanisms are not yet fully understood. To increase our understanding, variations of magnetic parameters are required. To that end, the magnetic semiconductor like (Ga,Mn)(As,P) are a good choice due to their magnetic properties easily adjustable thanks to the coupling betwee...
Trans-cis photoisomerization of azobenzene by n→π* excitation:A semiclassical dynamics study
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.
Magnetic correlation, excitation and slow dynamics in concentrated spin-glass alloys
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.
Semi-active control of dynamically excited structures using active interaction control
Zhang, Yunfeng
2001-01-01
This thesis presents a family of semi-active control algorithms termed Active Interaction Control (AIC) used for response control of dynamically excited structures. The AIC approach has been developed as a semiactive means of protecting building structures against large earthquakes. The AIC algorithms include the Active Interface Damping (AID), Optimal Connection Strategy (OCS), and newly developed Tuned Interaction Damping (TID) algorithms. All of the AIC algorithms are founded upon ...
Study on Dynamics of Polygonal Wear of Automotive Tire Caused by Self-Excited Vibration
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.
Dynamic correlation of photo-excited electrons: Anomalous levels induced by light–matter coupling
Nonlinear light–matter coupling plays an important role in many aspects of modern physics, such as spectroscopy, photo-induced phase transition, light-based devices, light-harvesting systems, light-directed reactions and bio-detection. However, excited states of electrons are still unclear for nano-structures and molecules in a light field. Our studies unexpectedly present that light can induce anomalous levels in the electronic structure of a donor–acceptor nanostructure with the help of the photo-excited electrons transferring dynamically between the donor and the acceptor. Furthermore, the physics underlying is revealed to be the photo-induced dynamical spin–flip correlation among electrons. These anomalous levels can significantly enhance the electron current through the nanostructure. These findings are expected to contribute greatly to the understanding of the photo-excited electrons with dynamic correlations, which provides a push to the development and application of techniques based on photosensitive molecules and nanostructures, such as light-triggered molecular devices, spectroscopic analysis, bio-molecule detection, and systems for solar energy conversion.
Dynamic performances of self-excited induction generator feeding different static loads
Nesba Ali
2006-01-01
Full Text Available The paper examines the dynamic performances of a three-phase self excited induction generator (SEIG during sudden connection of static loads. A dynamic flux model of the SEIG in the α-β axis stationary reference frame is presented. The main flux saturation effect in the SEIG is accounted for by using an accurate technique. The cases of purely resistive, inductive and capacitive load are amply discussed. Models for all of these three-phase load in the α-β axis stationary reference frame are also given. The analysis presented is validated experimentally.
Interplay between topology and dynamics in excitation patterns on hierarchical graphs
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.
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...
Shape dynamics of growing cell walls
Banerjee, Shiladitya; Scherer, Norbert F.; 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...
Kispersky, Tilman; White, John A.; Rotstein, Horacio G.
2010-01-01
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 fa...
Variation of Excited-State Dynamics in Trifluoromethyl Functionalized C60 Fullerenes
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.
Variation of excited-state dynamics in trifluoromethyl functionalized C60 fullerenes.
Park, Jaehong; Ramirez, Jessica J; Clikeman, Tyler T; Larson, Bryon W; Boltalina, Olga V; Strauss, Steven H; Rumbles, Garry
2016-08-17
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 (ΦISC), 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 ΦISC, therefore decreasing the average excited-state lifetime (τavg) by about 5 orders of magnitude compared to that of C60/4-1 and C60/6-2 (τavg ≈ 17 μs and 54 μs for C60/4-1 and C60/6-2, respectively, whereas τavg ≈ 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. PMID:27485768
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
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...
Steady-state responses of a belt-drive dynamical system under dual excitations
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.
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
The absorption and emission behaviour of flavin mononucleotide (FMN) in the wild-type light, oxygen and voltage-sensitive (LOV) domains LOV1 and LOV2 of the photoreceptor phot from the green alga Chlamydomonas reinhardtii is studied. FMN is non-covalently bound to the protein binding pocket of the LOV domains (LOV-ncb). Only a small amount of FMN is not bound in aqueous solution (LOV-ads). Blue-light photo-excitation of non-covalently bound FMN generates a non-fluorescent intermediate flavin-C(4a)-cysteinyl adduct, and concomitant blue-light adduct excitation converts it partly back to non-covalently bound FMN, thus hindering complete bound FMN transfer to the adduct form. The LOV domains with non-covalently bound FMN consist of two conformations, one with fast FMN-Cys adduct back recovery time to bound FMN (LOV-fast), and one with slow recovery time (LOV-slow) due to different activation barriers. Prolonged blue-light irradiation of the flavin-C(4a)-cysteinyl adducts reduces their ability to recover back in the dark. The photo-adduct formation in the LOV1 domains proceeds via triplet formation, while for the LOV2 domains the photo-adduct formation is thought to proceed via singlet excited-state electron transfer and singlet excited-state triplet formation. The photo-cycle dynamics of flavin-C(4a)-cysteinyl adduct formation and recovery is analysed
Photoluminescence and excited states dynamics in PbWO4:Pr3+ crystals
Auffray, E; Shalapska, T; Zazubovich, S
2014-01-01
Luminescence and photo-thermally stimulated defects creation processes are studied for a Pr3+-doped PbWO4 crystal at 4.2-400 K under excitation in the band-to-band, exciton, and charge-transfer transitions regions, as well as in the Pr3+-related absorption bands. Emission spectra of Pr3+ centers depend on the excitation energy, indicating the presence of Pr3+ centers of two types. The origin of these centers is discussed. The 2.03-2.06 eV emission, arising from the D-1(2) -> H-3(4) transitions of Pr3+ ions, is found to be effectively excited in a broad intense absorption band peaking at 4.2 K at 3.92 eV. By analogy with some other Pe(3+)-doped compounds, this band is suggested to arise from an electron transfer from an impurity Pr3+ ion to the crystal lattice W6+ or Pb2+ ions. The dynamics of the Pr3+-related excited states is clarified. In the PbWO4:Pr crystal studied, the concentration of single oxygen and lead vacancies as traps for electrons and holes is found to be negligible.
Dynamics of Below-Band-Gap Carrier in Highly Excited GaN
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.
Fidler, Andrew F.; Singh, Ved P.; Long, Phillip D.; Dahlberg, Peter D.; Engel, Gregory S.
2014-02-01
Time-resolved ultrafast optical probes of chiral dynamics provide a new window allowing us to explore how interactions with such structured environments drive electronic dynamics. Incorporating optical activity into time-resolved spectroscopies has proven challenging because of the small signal and large achiral background. Here we demonstrate that two-dimensional electronic spectroscopy can be adapted to detect chiral signals and that these signals reveal how excitations delocalize and contract following excitation. We dynamically probe the evolution of chiral electronic structure in the light-harvesting complex 2 of purple bacteria following photoexcitation by creating a chiral two-dimensional mapping. The dynamics of the chiral two-dimensional signal directly reports on changes in the degree of delocalization of the excitonic states following photoexcitation. The mechanism of energy transfer in this system may enhance transfer probability because of the coherent coupling among chromophores while suppressing fluorescence that arises from populating delocalized states. This generally applicable spectroscopy will provide an incisive tool to probe ultrafast transient molecular fluctuations that are obscured in non-chiral experiments.
Parak, W. J.; Domke, J; George, M.; Kardinal, A; Radmacher, M; Gaub, H E; Roos, A.D.; Theuvenet, A P; Wiegand, G.; Sackmann, E.; Behrends, J. C.
1999-01-01
In testing various designs of cell-semiconductor hybrids, the choice of a suitable type of electrically excitable cell is crucial. Here normal rat kidney (NRK) fibroblasts are presented as a cell line, easily maintained in culture, that may substitute for heart or nerve cells in many experiments. Like heart muscle cells, NRK fibroblasts form electrically coupled confluent cell layers, in which propagating action potentials are spontaneously generated. These, however, are not associated with m...
A theoretical study on the wavepacket dynamics in the excited states of aromatic biomolecules
The relaxation of the low-lying excited states of 9H-adenine through conical intersections of the dissociative “1πσ”* excited state with the lowest “1ππ”* excited state and the electronic-structure calculations and wave packet dynamics simulation. Adiabatic and quasidiabatic potential-energy surfaces and coupling elements were calculated as a function of the NH stretch coordinate of the azine group and the out-of-plane angle of the hydrogen atom, employing multireference configuration-interaction (MRCI) as well as restricted-active-space self-consistent-field (RASSCF) methods. Characteristic properties of the “1πσ”*-“1ππ”* and “1πσ”*-S0 conical intersections such as the diabatic-to-adiabatic mixing angle, the geometric phase of the adiabatic electronic wave functions, the derivative coupling, as well as adiabatic and diabatic trasition-dipole-moment surfaces were investigated in detail. Time-dependent wave packet simulations reveal an ultrafast relaxations dynamics of the optically-allowed lowest “1ππ”* state driven by vibronic coupling between strongly coupled electronic states that add to our understanding of the origin of the intrinsic photostability of the building blocks of life. (author)
Hou, H [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry
1995-12-01
This dissertation presents the results from the crossed molecular beam studies on the dynamics of bimolecular collisions in the gas phase. The primary subjects include the interactions of alkali dimer molecules with simple molecules, and the inelastic scattering of electronically excited alkali atoms with O_{2}. The reaction of the sodium dimers with oxygen molecules is described in Chapter 2. Two reaction pathways were observed for this four-center molecule-molecule reaction, i.e. the formations of NaO_{2} + Na and NaO + NaO. NaO_{2} products exhibit a very anisotropic angular distribution, indicating a direct spectator stripping mechanism for this reaction channel. The NaO formation follows the bond breaking of O_{2}, which is likely a result of a charge transfer from Na_{2} to the excited state orbital of O_{2-}. The scattering of sodium dimers from ammonium and methanol produced novel molecules, NaNH_{3} and Na(CH_{3}OH), respectively. These experimental observations, as well as the discussions on the reaction dynamics and the chemical bonding within these molecules, will be presented in Chapter 3. The lower limits for the bond dissociation energies of these molecules are also obtained. Finally, Chapter 4 describes the energy transfer between oxygen molecules and electronically excited sodium atoms.
Dissociation dynamics of simple chlorine containing molecules upon resonant Cl K-σ{sup *} excitation
Bohinc, R., E-mail: rok.bohinc@ijs.si; Bučar, K.; Kavčič, M. [Jožef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana (Slovenia); Žitnik, M. [Jožef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana (Slovenia); Faculty of Mathematics and Physics, University of Ljubljana, Jadranska ulica 19, SI-1000 Ljubljana (Slovenia)
2014-04-28
A theoretical analysis of dissociation dynamics of chlorine K-σ{sup *} core-excited molecules is performed. The potential energy surfaces of HCl, Cl{sub 2}, CH{sub 3}Cl, CH{sub 2}Cl{sub 2}, CHCl{sub 3}, CCl{sub 4}, CFCl{sub 3}, CF{sub 2}Cl{sub 2}, and CF{sub 3}Cl are calculated along the normal vibrational modes of the ground electronic state yielding the widths of the corresponding Franck-Condon distributions. An insight into the potential energy surface of 1st σ{sup *} resonances shows that the initial dissociation dynamics of chloro(fluoro)methanes mainly involves the distancing of the carbon and the core-excited chlorine atom and is practically independent of other atoms in the molecule, which is in agreement with the recent experimental findings. The carbon atom pulls out the remaining three atoms shortly after piercing the three-atom plane resulting in a high vibrationally excited state of the fragment if the reconnection time is smaller than the lifetime of the L shell.
Data-driven modelling of vertical dynamic excitation of bridges induced by people running
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.
Soliton-like excitation in a nonlinear model of DNA dynamics with viscosity.
Tabi, Conrad Bertrand; Mohamadou, Alidou; Kofane, Timoleon Crepin
2008-01-01
The study of solitary wave solutions is of prime significance for nonlinear physical systems. The Peyrard-Bishop model for DNA dynamics is generalized specifically to include the difference among bases pairs and viscosity. The small amplitude dynamics of the model is studied analytically and reduced to a discrete complex Ginzburg-Landau (DCGL) equation. Exact solutions of the obtained wave equation are obtained by the mean of the extended Jacobian elliptic function approach. These amplitude solutions are made of bubble solitons. The propagation of a soliton-like excitation in a DNA is then investigated through numerical integration of the motion equations. We show that discreteness can drastically change the soliton shape. The impact of viscosity as well as elasticity on DNA dynamic is also presented. The profile of solitary wave structures as well as the energy which is initially evenly distributed over the lattice are displayed for some fixed parameters. PMID:18193938
Fernandez-Alberti, Sebastian; Makhov, Dmitry V; Tretiak, Sergei; Shalashilin, Dmitrii V
2016-04-21
Photoinduced dynamics of electronic and vibrational unidirectional energy transfer between meta-linked building blocks in a phenylene ethynylene dendrimer is simulated using a multiconfigurational Ehrenfest in time-dependent diabatic basis (MCE-TDDB) method, a new variant of the MCE approach developed by us for dynamics involving multiple electronic states with numerous abrupt crossings. Excited-state energies, gradients and non-adiabatic coupling terms needed for dynamics simulation are calculated on-the-fly using the Collective Electron Oscillator (CEO) approach. A comparative analysis of our results obtained using MCE-TDDB, the conventional Ehrenfest method and the surface-hopping approach with and without decoherence corrections is presented. PMID:27004611
Dynamical resonance in F+H2 chemical reaction and rotational excitation effect
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.
Dynamic response of liquid-filled rectangular tank with elastic appendages under pitching excitation
L(U) Jing; LI Jun-feng; WANG Tian-shu
2007-01-01
Nonlinear dynamics of liquid-filled rectangular tank with elastic appendages are studied. Based on the assumption of ideal fluid, the coupling dynamic equations of rigid tank, elastic appendages and liquid fuel are derived using H-O principle. In the case of pitch excitation, the modified potential function and wave height function are introduced to describe the moving boundary of fluid, then Galerkin's method is used to discretize the dynamic equations into ordinary differential equations. The natural frequencies of the coupling system are formulated in liquid depth, the length of the tank,etc. The formulae are confirmed by numerical simulations, which also show that the effects of liquid and elastic appendages on the attitude angular of rigid.
Coupling dynamic analysis of a liquid-filled spherical container subject to arbitrary excitation
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.
Dynamic modification of the fragmentation of COq+ excited states generated with high-order harmonics
The dynamic process of fragmentation of COq+ excited states is investigated using a pump-probe approach. EUV radiation (32-48 eV) generated by high-order harmonics was used to ionize and excite CO molecules and a time-delayed infrared (IR) pulse (800 nm) was used to influence the evolution of the dissociating multichannel wave packet. Two groups of states, separable experimentally by their kinetic-energy release (KER), are populated by the EUV and lead to C+-O+ fragmentation: direct double ionization of the neutral molecule and fragmentation of the cation leading to C+-O*, followed by autoionization of O*. The IR pulse was found to modify the KER of the latter group in a delay-dependent way which is explained with a model calculation.
On the dynamics of excited atoms in time dependent electromagnetic fields
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
On the dynamics of excited atoms in time dependent electromagnetic fields
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
In this study, we investigate the accuracy of a recently developed coherent modified Redfield theory (CMRT) in simulating excitation energy transfer (EET) dynamics. The CMRT is a secular non-Markovian quantum master equation that is derived by extending the modified Redfield theory to treat coherence dynamics in molecular excitonic systems. Herein, we systematically survey the applicability of the CMRT in a large EET parameter space through the comparisons of the CMRT EET dynamics in a dimer system with the numerically exact results. The results confirm that the CMRT exhibits a broad applicable range and allow us to locate the specific parameter regimes where CMRT fails to provide adequate results. Moreover, we propose an accuracy criterion based on the magnitude of second-order perturbation to characterize the applicability of CMRT and show that the criterion summarizes all the benchmark results and the physics described by CMRT. Finally, we employ the accuracy criterion to quantitatively compare the performance of CMRT to that of a small polaron quantum master equation approach. The comparison demonstrates the complementary nature of these two methods, and as a result, the combination of the two methods provides accurate simulations of EET dynamics for the full parameter space investigated in this study. Our results not only delicately evaluate the applicability of the CMRT but also reveal new physical insights for factors controlling the dynamics of EET that should be useful for developing more accurate and efficient methods for simulations of EET dynamics in molecular aggregate systems
On the slow dynamics of near-field acoustically levitated objects under High excitation frequencies
Ilssar, Dotan; Bucher, Izhak
2015-10-01
This paper introduces a simplified analytical model describing the governing dynamics of near-field acoustically levitated objects. The simplification converts the equation of motion coupled with the partial differential equation of a compressible fluid, into a compact, second order ordinary differential equation, where the local stiffness and damping are transparent. The simplified model allows one to more easily analyse and design near-field acoustic levitation based systems, and it also helps to devise closed-loop controller algorithms for such systems. Near-field acoustic levitation employs fast ultrasonic vibrations of a driving surface and exploits the viscosity and the compressibility of a gaseous medium to achieve average, load carrying pressure. It is demonstrated that the slow dynamics dominates the transient behaviour, while the time-scale associated with the fast, ultrasonic excitation has a small presence in the oscillations of the levitated object. Indeed, the present paper formulates the slow dynamics under an ultrasonic excitation without the need to explicitly consider the latter. The simplified model is compared with a numerical scheme based on Reynolds equation and with experiments, both showing reasonably good results.
Han, Chul Hee [Sun Moon University, Asan (Korea, Republic of)
1995-11-15
It was well known that CT (Charge Transfer band) excitation of EDA (Electron Donor Acceptor) complex of Aromatic compound and Tetranitromethane (TNM) produces covalent adduct as the final product; however, it was not until the picosecond study on the Anthracene EDA complexes with Tetranitromethane that the dynamics associated with the covalent adduct formation and other related processes became quantitatively evaluated. According to the current understanding of the subject, picosecond excitation of EDA complex produces Contact Ion Pair (CIP) instantaneously, and this CIP is subject to two main competing processes; Ion-Pair collapse to form a covalent adduct and separation by solvent to form solvent separated Ion Pair (SSIP). In addition to these processes, Ion-pair exchange is possible with the added salt such as Tetra-n-butylammoniumperchlorate (TBA{sup +}P{sup -}) or Tetra-n-butyl-ammonium trinitromethide (TBA{sup +}T{sup -}). Previous picosecond study on the Anthracene EDA complexes with TNM employed a series of 9-X-anthracenes, where the substituents (X) of varying electrophilic character were used to modulate the ion-pair dynamics in various solvent with or without the added salts. Their work on the solvent effect and salt effect has revealed the importance of the ionic character of CIP in its solution dynamics.
It was well known that CT (Charge Transfer band) excitation of EDA (Electron Donor Acceptor) complex of Aromatic compound and Tetranitromethane (TNM) produces covalent adduct as the final product; however, it was not until the picosecond study on the Anthracene EDA complexes with Tetranitromethane that the dynamics associated with the covalent adduct formation and other related processes became quantitatively evaluated. According to the current understanding of the subject, picosecond excitation of EDA complex produces Contact Ion Pair (CIP) instantaneously, and this CIP is subject to two main competing processes; Ion-Pair collapse to form a covalent adduct and separation by solvent to form solvent separated Ion Pair (SSIP). In addition to these processes, Ion-pair exchange is possible with the added salt such as Tetra-n-butylammoniumperchlorate (TBA+P-) or Tetra-n-butyl-ammonium trinitromethide (TBA+T-). Previous picosecond study on the Anthracene EDA complexes with TNM employed a series of 9-X-anthracenes, where the substituents (X) of varying electrophilic character were used to modulate the ion-pair dynamics in various solvent with or without the added salts. Their work on the solvent effect and salt effect has revealed the importance of the ionic character of CIP in its solution dynamics.
Novoderezhkin, Vladimir I; Doust, Alexander B; Curutchet, Carles; Scholes, Gregory D; van Grondelle, Rienk
2010-07-21
We model the spectra and excitation dynamics in the phycobiliprotein antenna complex PE545 isolated from the unicellular photosynthetic cryptophyte algae Rhodomonas CS24. The excitonic couplings between the eight bilins are calculated using the CIS/6-31G method. The site energies are extracted from a simultaneous fit of the absorption, circular dichroism, fluorescence, and excitation anisotropy spectra together with the transient absorption kinetics using the modified Redfield approach. Quantitative fit of the data enables us to assign the eight exciton components of the spectra and build up the energy transfer picture including pathways and timescales of energy relaxation, thus allowing a visualization of excitation dynamics within the complex. PMID:20643051
Optimal placement of excitations and sensors for verification of large dynamical systems
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.
Decay dynamics of excited CS2 and NH3 investigated by femtosecond laser
无
2002-01-01
By using the home-made femtosecond laser system and the time-of-flightmass spectrometer, the decay dynamics of excited carbon disulfide (CS2) and ammonia (NH3) are investigated in real time by pump-probe multiphoton ionization detection. The estimated lifetime constant of the NH3 state (514 fs) agreed quite well with the literature report. For the first time, the decay lifetime constants of the NH3 ′1A′1 state (93793 fs), the CS2 state (153 ± 10 fs), and the CS2 Rydberg state[2-3]6sσg(3Ⅱg)(948 ± 23 fs) are obtained.
We report large effects of Parisi replica permutation symmetry breaking (RPSB) on elementary excitations of fermionic systems with frustrated magnetic interactions. The electronic density of states is obtained exactly in the zero temperature limit for (K = 1)- step RPSB together with relations for arbitrary breaking K, which lead to a new fermionic and dynamical Parisi solution at K = ∞. The Ward identity for charge conservation indicates RPSB-effects on the conductivity in metallic quantum spin glasses. This implies that RPSB is essential for any fermionic system showing spin glass sections within its phase diagram. An astonishing similarity with a neural network problem is also observed. (author)
Kaiyun Wang
2016-01-01
Full Text Available Spalling in contact surface of rail is a typical form of rolling contact fatigue, which is a difficult problem to solve in railway. Once the spalling occurs in the rail, the wheel-rail dynamic interaction will become more severe. The wheel-rail dynamic interaction is investigated based on the theory of vehicle-track coupled dynamics in this paper, where the excitation modes of the rail spalling failure are taken into consideration for high-speed wheel-rail system. A modified excitation model of rail spalling failure is proposed. It can enable the investigations on two kinds of excitation modes in wheel-rail system due to the rail spalling, including the pulse and the harmonic excitation modes. The excitation mode can be determined by the ratio of the spalling length to its critical length. Thus, the characteristics of wheel-rail dynamic vibration excited by two kinds of excitation are simulated in detail. Consequently, the limited value of the spalling length is suggested for high-speed railway.
Synchronization phenomena in mixed media of passive, excitable, and oscillatory cells
Kryukov, A. K.; Petrov, V. S.; Averyanova, L. S.; Osipov, G. V.; Chen, W.; Drugova, O.; Chan, C. K.
2008-09-01
We study collective phenomena in highly heterogeneous cardiac cell culture and its models. A cardiac culture is a mixture of passive (fibroblasts), oscillatory (pacemakers), and excitable (myocytes) cells. There is also heterogeneity within each type of cell as well. Results of in vitro experiments are modelled by Luo-Rudy and FitzHugh-Nagumo systems. For oscillatory and excitable media, we focus on the transitions from fully incoherent behavior to partially coherent behavior and then to global synchronization as the coupling strength is increased. These regimes are characterized qualitatively by spatiotemporal diagrams and quantitatively by profiles of dependence of individual frequencies on coupling. We find that synchronization clusters are determined by concentric and spiral waves. These waves arising due to the heterogeneity of medium push covered cells to oscillate in synchrony. We are also interested in the influence of passive and excitable elements on the oscillatory characteristics of low- and high-dimensional ensembles of cardiac cells. The mixture of initially silent excitable and passive cells shows the transitions to oscillatory behavior. In the media of oscillatory and passive or excitable cells, the effect of oscillation death is observed.
Shape dynamics of growing cell walls
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...
Tian, L.; Wang, W. J.; Peng, Z. J.
2011-09-01
The rotor dynamic behaviour of turbochargers (TC) has been paid significant attention because of its importance in their healthy operation. Commonly, the TC is firmly mounted on engines and they will definitely suffer from the vibrations originated from engines in operation. However, only a limited number of papers have been published with consideration of this phenomenon. In this paper, a finite element model of a TC rotor supported by nonlinear floating ring bearings has been established. The nonlinear bearing forces have been calculated by a newly proposed analytical method. An efficient numerical integration approach has been employed to conduct the investigation including the traditional unbalance and the considered engine excitation effects in question. The results show that the unbalance will place considerable influence on the rotor response at a low working speed. At high speeds, the effect will be prevented by the dominant sub-synchronous vibrations, which also prohibit the appearance of a chaotic state. The novel investigation with the proposed model considering engine excitation reveals that the engine induced vibration will greatly affect the TC rotor response at relatively lower rotor speeds as well. At higher speed range, the dominant effect of sub-synchronous vibrations is still capable of keeping the same orbit shapes as that without engine excitation from a relative viewpoint.
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 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
Complex dynamics of an archetypal self-excited SD oscillator driven by moving belt friction
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).
Cao, Jun; Xie, Zhi-Zhong; Yu, Xiaodong
2016-08-01
In the present work, the combined electronic structure calculations and surface hopping simulations have been performed to investigate the excited-state decay of the parent oxazole in the gas phase. Our calculations show that the S2 state decay of oxazole is an ultrafast process characterized by the ring-opening and ring-closure of the five-membered oxazole ring, in which the triplet contribution is minor. The ring-opening involves the Osbnd C bond cleavage affording the nitrile ylide and airine intermediates, while the ring-closure gives rise to a bicyclic species through a 2sbnd 5 bond formation. The azirine and bicyclic intermediates in the S0 state are very likely involved in the phototranspositions of oxazoles. This is different from the previous mechanism in which these intermediates in the T1 state have been proposed for these phototranspositions.
Taniguchi, Daisuke; Ishihara, Shuji; Oonuki, Takehiko; Honda-Kitahara, Mai; Kaneko, Kunihiko; Sawai, Satoshi
2013-03-26
In both randomly moving Dictyostelium and mammalian cells, phosphatidylinositol (3,4,5)-trisphosphate and F-actin are known to propagate as waves at the membrane and act to push out the protruding edge. To date, however, the relationship between the wave geometry and the patterns of amoeboid shape change remains elusive. Here, by using phase map analysis, we show that morphology dynamics of randomly moving Dictyostelium discoideum cells can be characterized by the number, topology, and position of spatial phase singularities, i.e., points that represent organizing centers of rotating waves. A single isolated singularity near the cellular edge induced a rotational protrusion, whereas a pair of singularities supported a symmetric extension. These singularities appeared by strong phase resetting due to de novo nucleation at the back of preexisting waves. Analysis of a theoretical model indicated excitability of the system that is governed by positive feedback from phosphatidylinositol (3,4,5)-trisphosphate to PI3-kinase activation, and we showed experimentally that this requires F-actin. Furthermore, by incorporating membrane deformation into the model, we demonstrated that geometries of competing waves explain most of the observed semiperiodic changes in amoeboid morphology. PMID:23479620
Electron dynamics and prompt ablation of aluminum surface excited by intense femtosecond laser pulse
Ionin, A. A.; Kudryashov, S. I.; Makarov, S. V.; Seleznev, L. V.; Sinitsyn, D. V.
2014-12-01
Thin aluminum film homogeneously heated by intense IR femtosecond laser pulses exhibits on the excitation timescale consequent fluence-dependent rise and drop of the IR-pump self-reflectivity, followed by its final saturation at higher fluences F > 0.3 J/cm2. This prompt optical dynamics correlates with the initial monotonic increase in the accompanying laser-induced electron emission, which is succeeded by its non-linear (three-photon) increase for F > 0.3 J/cm2. The underlying electronic dynamics is related to the initial saturation of IR resonant interband transitions in this material, followed by its strong instantaneous electronic heating via intraband transitions during the pump pulse resulting in thermionic emission. Above the threshold fluence of 0.3 J/cm2, the surface electronic heating is balanced during the pump pulse by simultaneous cooling via intense plasma removal (prompt ablation). The relationship between the deposited volume energy density in the film and its prompt electronic temperature derived from the self-reflection measurements using a Drude model, demonstrates a kind of electron "liquid-vapor" phase transition, driven by strong cubic optical non-linearity of the photo-excited aluminum.
Dynamics of the excitation of an upper hybrid wave by a rippled laser beam in magnetoplasma
This paper presents the effects of a laser spike (superimposed on an intense laser beam) and a static magnetic field on the excitation of the upper hybrid wave (UHW) in a hot collisionless magnetoplasma, taking into account the relativistic nonlinearity. The laser beam is propagating perpendicular to the static magnetic field and has its electric vector polarized along the direction of the static magnetic field (ordinary mode). Analytical expressions for the growth rate of the ripple, the beam width of the rippled laser beam, and the UHW have been obtained. It is found that the coupling among the main laser beam, ripple, and UHW is strong. The ripple gets focused when the initial power of the laser beam is greater than the critical power for focusing. It has been shown that the presence of a laser spike affects significantly the growth rate and the dynamics of the UHW. In addition, it has been seen that the effect of changing the strength of the static magnetic field on the nonlinear coupling and on the dynamics of the excitation of the UHW is significant. The results are presented for typical laser plasma parameters
Excited-state dynamics of size-dependent colloidal TiO2-Au nanocomposites
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.
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.
Effect of CH stretching excitation on the reaction dynamics of F + CHD3 → DF + CHD2
The vibrationally excited reaction of F + CHD3(ν1 = 1) → DF + CHD2 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 CHD3 reagent in the crossed-beam region. It is found that all vibrational states of the CHD2 products observed in the ground-state reaction, which mainly involve the excitation of the umbrella mode of the CHD2 products, are severely suppressed by the CH stretching excitation. However, there are four additional vibrational states of the CHD2 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 CHD2 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
Regulation of granule cell excitability by a low-threshold calcium spike in turtle olfactory bulb
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 of...
Adhikari, Aniruddha; Sahu, Kalyanasis; Dey, Shantanu; Ghosh, Subhadip; Mandal, Ujjwal; Bhattacharyya, Kankan
2007-11-01
Solvation dynamics in a neat ionic liquid, 1-pentyl-3-methyl-imidazolium tetra-flouroborate ([pmim][BF4]) and its microemulsion in Triton X-100 (TX-100)/benzene is studied using femtosecond up-conversion. In both the neat ionic liquid and the microemulsion, the solvation dynamics is found to depend on excitation wavelength (lambda(ex)). The lambda(ex) dependence is attributed to structural heterogeneity in neat ionic liquid (IL) and in IL microemulsion. In neat IL, the heterogeneity arises from clustering of the pentyl groups which are surrounded by a network of cation and anions. Such a nanostructural organization is predicted in many recent simulations and observed recently in an X-ray diffraction study. In an IL microemulsion, the surfactant (TX-100) molecules aggregate in form of a nonpolar peripheral shell around the polar pool of IL. The micro-environment in such an assembly varies drastically over a short distance. The dynamic solvent shift (and average solvation time) in neat IL as well as in IL microemulsions decreases markedly as lambda(ex) increases from 375 to 435 nm. In a [pmim][BF4]/water/TX-100/benzene quaternary microemulsion, the solvation dynamics is slower than that in a microemulsion without water. This is ascribed to the smaller size of the water containing microemulsion. The anisotropy decay in an IL microemulsion is found to be faster than that in neat IL. PMID:17944511
Global Dynamic Characteristic of Nonlinear Torsional Vibration System under Harmonically Excitation
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.
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
The problem of nonlocality in the dynamical three-body Casimir-Polder interaction between an initially excited and two ground-state atoms is considered. It is shown that the nonlocal spatial correlations of the field emitted by the excited atom during the initial part of its spontaneous decay may become manifest in the three-body interaction. The observability of this new phenomenon is discussed
Epigenetic dynamics across the cell cycle
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....
Electric dipole versus full interaction in the dynamics of laser excitation of Rydberg wavepackets
We solve the time-dependent Schroedinger equation (TDSE) that describes the resonant excitation of the hydrogen 1s state to Rydberg states and wavepackets using the electric dipole approximation (EDA) in the length form as well as the full electric interaction of the multipolar Hamiltonian. The time-dependent wavefunctions are expanded in a hydrogenic basis and the TDSE is transformed into a system of coupled integro-differential equations. The truncation of this expansion is done systematically and judiciously within a scheme which we call the multimanifold intrashell approximation, according to which the intershell matrix elements are ignored. The ensuing drastic reduction in the size of the overall calculation allows an economic and meaningful solution of the problem when the multipolar interaction to all orders is taken into account. Three categories of calculations were carried out, all involving many hydrogenic n-manifolds, without and with intrashell couplings. A series of computations dealt with resonant excitation of manifolds up to nres=85. The first two categories of calculations involved the EDA and multimanifold expansions without and with intrashell matrix elements. The third category involved the full multipolar interaction and multimanifold expansions with intrashell matrix elements. The reported time-dependent survival probabilities revealed that, even for the weak field used (8.75x107 W cm-2), as the level of the resonant excitation rises beyond n≥10, the EDA fails to describe the correct dynamics of such processes. The results herein provide quantitative information and demonstrate beyond doubt the limitations and inaccuracies of the EDA when the field-atom coupling involves extended wavefunctions, such as the high-lying Rydberg states. (author)
Full text: Intense irradiation of matter with femtosecond laser light leads to electric forces that exceed those that bind matter. Such interaction can be studied with high precision and little energy, and it causes highly non-linear processes like high order harmonic generation, x-ray production, production of very fast particles, Coulomb explosion of molecules, etc. For very short pulses the molecular response is dominated by the electrons. The resulting non-adiabatic multi-electron dynamics plays a central role in the efficiency of light absorption and conversion into kinetic energy of the resulting particles. Recent experimental and theoretical results concerned with this subject will be reviewed. They demonstrate on one side that complex multi-electron dynamics is responsible for efficient absorption and high energy conversion if clusters are used as a molecular target. On the other side, for single molecules popular quasi-static models for strong field-ionization processes become useless if the delocalized electron path within the molecule exceeds a limiting length. In such cases the resulting excitation and fragmentation become very strong, which has important consequences for many applications of femtosecond pulses, from controlling molecular dynamics to mass spectrometry. Refs. 2 (author)
Dynamics of laser excited colloidal gold nanoparticles functionalized with cysteine derivatives
The ultrafast dynamics of Au colloidal nanoparticles excited with femtosecond laser pulses is investigated experimentally. The transient absorption signal presents a bleaching of the surface plasmon band and a transient absorption at the wings of the band. The kinetics of the “hot” electrons in Au nanoparticles show a fast component of around 1 ps and a slower one of approximately 300 ps. Additionally, we found that the time of the ground state population recovery of Au nanoparticles depends on the pump wavelength. Furthermore, the interaction of Au nanoparticles with cysteine and cystine is studied at different pump wavelengths. The increase of the ligand concentration produces a variation of the relaxation times, as well as a delay of the time zero kinetics due to the adsorption of the ligands to the Au surface. - Highlights: • The ultrafast dynamics of AuNPs were investigated using femtosecond laser pulses. • The “hot” electrons dynamics shows two components: fast (1 ps) and slow (300 ps). • We studied the transient absorption behavior of the S-ligands functionalized AuNPs. • The relaxation times varied with increasing the ligand fraction
Graphical abstract: Dynamical calculations on an asymmetric rotor are made to ascertain the rate of internal conversion after photo-excitation. The rate depends heavily on the modes included. Abstract: The excited state dynamics of 2-cyclopentylidene-tetrahydrofuran (CPTHF) is investigated using quantum dynamics. CPTHF can be considered a model for an asymmetric molecular rotor in which unidirectional rotation could be triggered around the double bond. After excitation, conical intersections at twisted angles allow for rationless decay to the ground state. Two-dimensional potential energy surfaces for the ground and first (ππ*) excited state have been calculated using CASSCF. They include the torsion around the double bond and the pyramidalisation at one carbon atom. The relaxation of CPTHF after photo-excitation has been then studied using up to five degrees of freedom. 2D wavepacket propagations on the explicit PESs do not allow the dissipation of the energy of the system after excitation. The inclusion of further modes, studied using the MCTDH method, show that the internal conversion rate is significantly altered depending on the modes included.
The formation of electronically excited species in the human multiple myeloma cell suspension
Rác, Marek; Sedlářová, Michaela; Pospíšil, Pavel
2015-01-01
In this study, evidence is provided on the formation of electronically excited species in human multiple myeloma cells U266 in the growth medium exposed to hydrogen peroxide (H2O2). Two-dimensional imaging of ultra-weak photon emission using highly sensitive charge coupled device camera revealed that the addition of H2O2 to cell suspension caused the formation of triplet excited carbonyls 3(R = O)*. The kinetics of 3(R = O)* formation in the real time, as measured by one-dimensional ultra-wea...
Mohamed E. A. Farrag
2014-01-01
Full Text Available Incentives, such as the Feed-in-tariff are expected to lead to continuous increase in the deployment of Small Scale Embedded Generation (SSEG in the distribution network. Self-Excited Induction Generators (SEIG represent a significant segment of potential SSEG. The quality of SEIG output voltage magnitude and frequency is investigated in this paper to support the SEIG operation for different network operating conditions. The dynamic behaviour of the SEIG resulting from disconnection, reconnection from/to the grid and potential operation in islanding mode is studied in detail. The local load and reactive power supply are the key factors that determine the SEIG performance, as they have significant influence on the voltage and frequency change after disconnection from the grid. Hence, the aim of this work is to identify the optimum combination of the reactive power supply (essential for self excitation of the SEIG and the active load (essential for balancing power generation and demand. This is required in order to support the SEIG operation after disconnection from the grid, during islanding and reconnection to the grid. The results show that the generator voltage and speed (frequency can be controlled and maintained within the statuary limits. This will enable safe disconnection and reconnection of the SEIG from/to the grid and makes it easier to operate in islanding mode.
Classical, non-linear, internal dynamics of large, isolated, vibrationally excited molecules
Papoular, R J
2002-01-01
This work reports numerical experiments intended to clarify the internal equilibration process in large molecules, following vibrational excitation. A model of amorphous and oxygenated hydrocarbon macromolecule (about 500 atoms)--simulating interstellar dust-- is built up by means of a chemical simulation code. Its structure is optimized, and its normal modes determined. About 4.5 eV of potential energy is then deposited locally by perturbing one of the C-H peripheral bonds, thus simulating the capture of a free H atom by a dangling C bond. The ensuing relaxation of the system is followed for up to 300 ps, using a molecular mechanics code. When steady state is reached, spectra and time correlation functions of kinetic energy and bond length fluctuations indicate that most normal modes have been activated, but the motion remains quasi-periodic or regular. By contrast, when the molecule is violently excited or embedded in a thermal bath (modelled by Langevin dynamics), the same markers clearly depict chaotic mo...
Dynamic Balance of Excitation and Inhibition in Human and Monkey Neocortex
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.
KEWPIE2: A cascade code for the study of dynamical decay of excited nuclei
Lü, Hongliang; Marchix, Anthony; Abe, Yasuhisa; Boilley, David
2016-03-01
KEWPIE-a cascade code devoted to investigating the dynamical decay of excited nuclei, specially designed for treating very low probability events related to the synthesis of super-heavy nuclei formed in fusion-evaporation reactions-has been improved and rewritten in C++ programming language to become KEWPIE2. The current version of the code comprises various nuclear models concerning the light-particle emission, fission process and statistical properties of excited nuclei. General features of the code, such as the numerical scheme and the main physical ingredients, are described in detail. Some typical calculations having been performed in the present paper clearly show that theoretical predictions are generally in accordance with experimental data. Furthermore, since the values of some input parameters cannot be determined neither theoretically nor experimentally, a sensibility analysis is presented. To this end, we systematically investigate the effects of using different parameter values and reaction models on the final results. As expected, in the case of heavy nuclei, the fission process has the most crucial role to play in theoretical predictions. This work would be essential for numerical modeling of fusion-evaporation reactions.
Origin of long-lived coherence and excitation dynamics in pigment-protein complexes
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.
PATH INTEGRAL SOLUTION OF NONLINEAR DYNAMIC BEHAVIOR OF STRUCTURE UNDER WIND EXCITATION
无
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.
Dynamic responses of base isolated NPPs under seismic excitations and aircraft crashes
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
Dynamics of multiple bubbles, excited by femtosecond filament in water: Role of aberrations
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...
Ultrafast Nonlinear Excitation Dynamics of Black Phosphorus Nanosheets from Visible to Mid-Infrared.
Wang, Kangpeng; Szydłowska, Beata M; Wang, Gaozhong; Zhang, Xiaoyan; Wang, Jing Jing; Magan, John J; Zhang, Long; Coleman, Jonathan N; Wang, Jun; Blau, Werner J
2016-07-26
The recent progress on black phosphorus makes it a promising candidate material for broadband nanophotonic devices, especially operating in the mid-infrared spectral region. Here, the excited carrier dynamics and nonlinear optical response of unoxidized black phosphorus nanosheets and their wavelength dependence were systematically studied from 800 nm to 2.1 μm. The wavelength-dependent relaxation times of black phosphorus nanosheets are determined to be 360 fs to 1.36 ps with photon energies from 1.55 to 0.61 eV. In a comparative study with graphene, we found that black phosphorus has a faster carrier relaxation in near- and mid-infrared region. With regard to nonlinear optical absorption, the response of black phosphorus significantly increases from near- to mid-infrared, and black phosphorus is also confirmed to be better as saturable absorber to MoS2 in infrared region. PMID:27281449
Meenehan, Seán M.; Cohen, Justin D.; MacCabe, Gregory S.; Marsili, Francesco; Shaw, Matthew D.; Painter, Oskar
2015-10-01
Using pulsed optical excitation and read-out along with single-phonon-counting techniques, we measure the transient backaction, heating, and damping dynamics of a nanoscale silicon optomechanical crystal cavity mounted in a dilution refrigerator at a base temperature of Tf≈11 mK . In addition to observing a slow (approximately 740-ns) turn-on time for the optical-absorption-induced hot-phonon bath, we measure for the 5.6-GHz "breathing" acoustic mode of the cavity an initial phonon occupancy as low as ⟨n ⟩=0.021 ±0.007 (mode temperature Tmin≈70 mK ) and an intrinsic mechanical decay rate of γ0=328 ±14 Hz (Qm≈1.7 ×107). 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.
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.