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Artykuły w czasopismach na temat "Oscillation mode transition"
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LEONTINI, JUSTIN S., M. C. THOMPSON i K. HOURIGAN. "Three-dimensional transition in the wake of a transversely oscillating cylinder". Journal of Fluid Mechanics 577 (19.04.2007): 79–104. http://dx.doi.org/10.1017/s0022112006004320.
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A Floquet stability analysis of the transition to three-dimensionality in the wake of a cylinder forced to oscillate transversely to the free stream has been undertaken. The effect of varying the oscillation amplitude is determined for a frequency of oscillation close to the natural shedding frequency. The three-dimensional modes that arise are identified, and the effect of the oscillation amplitude on their structure and growth rate quantified.It is shown that when the two-dimensional wake is in the 2S configuration (which is similar to the Kármán vortex street), the three-dimensional modes that arise are similar in nature and symmetry structure to the modes in the wake of a fixed cylinder. These modes are known as modes A, B and QP and occur in this order with increasing Re. However, increasing the amplitude of oscillation causes the critical Reynolds number for mode A to increase significantly, to the point where mode B becomes critical before mode A. The critical wavelength for mode A is also affected by the oscillation, becoming smaller with increasing amplitude. Elliptic instability theory is shown also to predict this trend, providing further support that mode A primarily arises as a result of an elliptic instability.At higher oscillation amplitudes, the spatio-temporal symmetry of the two-dimensional wake changes and it takes on the P + S configuration, with a pair of vortices on one side of the wake and a single vortex on the other side, for each oscillation cycle. With the onset of this configuration, modes A, B and QP cease to exist. It is shown that two new three-dimensional modes arise from this base flow, which we call modes SL and SS. Both of these modes are subharmonic, repeating over two base-flow periods. Also, either mode can be the first to become critical, depending on the amplitude of oscillation of the cylinder.The emergence of these two new modes, as well as the reversal of the order of inception of the three-dimensional modes A and B, leads to the observation that for an oscillating cylinder wake there are four different modes that can lead the transition to three-dimensionality, depending on the amplitude of oscillation. Therefore this type of flow provides a good example for studying the effect of mode-order inception on the path taken to turbulence in bluff-body wakes.For the range of amplitudes studied, the maximum Re value for which the flow remains two-dimensional is 280.
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Ren, Linyuan, Yanan Wang, Weidong Ding, Anbang Sun, Burak Karadag, Zichen Deng i Jinyue Geng. "Discharge characteristics and mode transition of a ring-cusp magnetically confined plasma bridge neutralizer". Journal of Applied Physics 132, nr 8 (28.08.2022): 083301. http://dx.doi.org/10.1063/5.0101904.
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The discharge mode characteristics of cathodes may strongly influence the discharge stability and performance of electrostatic thrusters. In this article, discharge characteristics and mode transition phenomenon of the ring-cusp magnetically confined plasma bridge neutralizer (RCM-PBN) were experimentally studied using argon as the working gas. The dependences of anode current and oscillation amplitude on anode voltage, argon flow rate, heater power, and cathode-to-anode distance were investigated. Plasma properties were measured and plasma plume images were taken under different discharge modes. Two distinct discharge modes were observed during the experiments: high oscillation mode and low oscillation mode. In the high oscillation mode, the plasma plume appears dim, the anode current is low, and the oscillation level is more than 2%. While in the low oscillation mode, a spot-like structure close to the orifice is observed. The plume becomes brighter, the anode current increases, and the oscillation level decreases below 2%. The RCM-PBN was found to transition into the low oscillation mode by increasing anode voltage, flow rate, heater power and by decreasing the cathode-to-anode distance.
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Boriskov, Petr, Andrei Velichko, Nikolay Shilovsky i Maksim Belyaev. "Bifurcation and Entropy Analysis of a Chaotic Spike Oscillator Circuit Based on the S-Switch". Entropy 24, nr 11 (19.11.2022): 1693. http://dx.doi.org/10.3390/e24111693.
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This paper presents a model and experimental study of a chaotic spike oscillator based on a leaky integrate-and-fire (LIF) neuron, which has a switching element with an S-type current-voltage characteristic (S-switch). The oscillator generates spikes of the S-switch in the form of chaotic pulse position modulation driven by the feedback with rate coding instability of LIF neuron. The oscillator model with piecewise function of the S-switch has resistive feedback using a second order filter. The oscillator circuit is built on four operational amplifiers and two field-effect transistors (MOSFETs) that form an S-switch based on a Schmitt trigger, an active RC filter and a matching amplifier. We investigate the bifurcation diagrams of the model and the circuit and calculate the entropy of oscillations. For the analog circuit, the “regular oscillation-chaos” transition is analysed in a series of tests initiated by a step voltage in the matching amplifier. Entropy values are used to estimate the average time for the transition of oscillations to chaos and the degree of signal correlation of the transition mode of different tests. Study results can be applied in various reservoir computing applications, for example, in choosing and configuring the LogNNet network reservoir circuits.
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Cai, M. L., Z. D. Liu, Y. Jiang, Y. K. Wu, Q. X. Mei, W. D. Zhao, L. He, X. Zhang, Z. C. Zhou i L. M. Duan. "Probing a Dissipative Phase Transition with a Trapped Ion through Reservoir Engineering". Chinese Physics Letters 39, nr 2 (1.02.2022): 020502. http://dx.doi.org/10.1088/0256-307x/39/2/020502.
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Dissipation is often considered as a detrimental effect in quantum systems for unitary quantum operations. However, it has been shown that suitable dissipation can be useful resources in both quantum information and quantum simulation. Here, we propose and experimentally simulate a dissipative phase transition (DPT) model using a single trapped ion with an engineered reservoir. We show that the ion’s spatial oscillation mode reaches a steady state after the alternating application of unitary evolution under a quantum Rabi model Hamiltonian and sideband cooling of the oscillator. The average phonon number of the oscillation mode is used as the order parameter to provide evidence for the DPT. Our work highlights the suitability of trapped ions for simulating open quantum systems and shall facilitate further investigations of DPT with various dissipation terms.
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KANO, HIDEAKI, TAKASHI SAITO, AKIKATSU UEKI i TAKAYOSHI KOBAYASHI. "FIRST OBSERVATION OF DYNAMIC INTENSITY BORROWING INDUCED BY COHERENT MOLECULAR VIBRATIONS IN J-AGGREGATES REVEALED BY SUB-5-FS SPECTROSCOPY". International Journal of Modern Physics B 15, nr 28n30 (10.12.2001): 3817–20. http://dx.doi.org/10.1142/s0217979201008743.
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Sub-5-fs spectroscopy of porphyrin J-aggregates reveals for the first time coherent molecular vibration coupled to the Frenkel exciton. The oscillations with the frequency of 244cm-1 are described by a plus-cosine function for bleaching and a minus-cosine function for induced absorption. The coherent oscillation is explained by a modulated transition dipole moment, which is due to the transfer of an oscillator strength from the intense B-band to the weak Q-band through the ruffling mode with 244cm-1-frequency.
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Kikteva V. R., Kiseleva K. V., Kichin G. A., Skirdkov P. N. i Zvezdin K. A. "Impact of the mutual direction of Polarizer and Free Layer on the auto-oscillation mode of magnetic tunnel junctions (MTJs) of different geometry". Physics of the Solid State 65, nr 6 (2023): 893. http://dx.doi.org/10.21883/pss.2023.06.56097.03h.
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In this work we studied the auto-oscillation mode of structures based on magnetic tunnel junctions. During the experiment we studied how different values and orientation of the magnetic field affect the efficiency of the auto-oscillations regime for samples of various shapes. The auto-oscillation mode in samples was observed near the transition from one state of magnetization of the free layer to another. It was found that the maximum value of the power spectral density and its position relative to the frequency axis can be controlled by changing the magnitude and orientation of the external magnetic field. Keywords: Magnetic tunnel junction (MTJ), auto-oscillations, power spectral density, nanooscillator.
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Smirnov, Alexey, i Boris Smolnikov. "COLLINEAR CONTROL OF OSCILLATION MODES OF SPATIAL DOUBLE PENDULUM WITH VARIABLE GAIN". Cybernetics and Physics, Volume 10, 2021, Number 2 (1.10.2021): 88–96. http://dx.doi.org/10.35470/2226-4116-2021-10-2-88-96.
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This article is devoted to the study of controlled movements of spatial double pendulum with non-parallel cylindrical joints axes. The collinear control is used to swinging of the system by feedback. The most important property of collinear control is the ability of increasing system oscillations only on one oscillation mode. A modification of the collinear control law with variable gain depending on the energy level is investigated. It allows to control the system motions more flexible than in the case of constant gain. As a result, it is possible to observe a smooth transition from a linear oscillation mode to a nonlinear one with a gradual output to a steady oscillation motion with a given energy level. The obtained results are clearly illustrated by graph dependencies that demonstrate the swinging of the system on one oscillation mode from small to finite amplitudes.
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HASEGAWA, YOSHITAKA, RYUICHIRO TANAKA i YOSHISUKE UEDA. "ON RATIONAL PHASE-LOCKING OSCILLATIONS OF A SIMPLE SAWTOOTH OSCILLATOR WITH UJT". International Journal of Bifurcation and Chaos 11, nr 12 (grudzień 2001): 3003–32. http://dx.doi.org/10.1142/s0218127401004121.
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There are some reports about sawtooth oscillations on various systems. The authors constructed the sawtooth oscillator circuit exploiting a Uni-Junction Transistor (UJT), and investigated various nonautonomous-like oscillations induced by an external sinusoidal input. Different from the cases of ordinary differential equation (ODE) systems driven with some periodic oscillation, this input periodically alternates only the threshold of the mode transition. Many systems in various fields of electrical circuits, biology and so on utilize threshold variation or modulation between operational modes, and our system is a very simple representative. Though our circuit behaves as a piecewise-continuous ODE system, we will suggest one-dimensional map depending on the phase of the external sinusoidal input. And we will study the background about the existence of various rational locking mode in the analytic method, numerical investigations and circuit experiments, identifying our system as a discrete dynamical system. This paper reveals not only the existing regions of the respective modes, but also reports about respective itineraries of periodic solutions geometrically. Readers will see that the mode distribution constitutes a Cantor set structure.
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Iga, Keita. "Transition modes of rotating shallow water waves in a channel". Journal of Fluid Mechanics 294 (10.07.1995): 367–90. http://dx.doi.org/10.1017/s002211209500293x.
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Normal modes of shallow water waves in a channel wherein the Coriolis parameter and the depth vary in the spanwise direction are investigated based on the conservation of the number of zeros in an eigenfunction. As a result, it is generally shown that the condition for transition modes (Kelvin modes and mixed Rossby-gravity modes) to exist, besides Rossby and Poincaré modes, is determined only by boundary conditions. A Kelvin mode is interpreted as a modification of a Kelvin wave or a boundary wave along a closed boundary, and a mixed Rossby-gravity mode as a modification of an inertial oscillation or a boundary wave along an open boundary. Transition modes appearing in edge and continental-shelf waves, equatorial waves and free oscillations over a sphere are systematically understood by applying the theory in this paper.
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Aoyagi, Toshio, Takashi Takekawa i Tomoki Fukai. "Gamma Rhythmic Bursts: Coherence Control in Networks of Cortical Pyramidal Neurons". Neural Computation 15, nr 5 (1.05.2003): 1035–61. http://dx.doi.org/10.1162/089976603765202659.
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Much evidence indicates that synchronized gamma-frequency (20–70 Hz) oscillation plays a significant functional role in the neocortex and hippocampus. Chattering neuron is a possible neocortical pacemaker for the gamma oscillation. Based on our recent model of chattering neurons, here we study how gamma-frequency bursting is synchronized in a network of these neurons. Using a phase oscillator description, we first examine how two coupled chattering neurons are synchronized. The analysis reveals that an incremental change of the bursting mode, such as from singlet to doublet, always accompanies a rapid transition from antisynchronous to synchronous firing. The state transition occurs regardless of what changes the bursting mode. Within each bursting mode, the neuronal activity undergoes a gradual change from synchrony to antisynchrony. Since the sensitivity to Ca2+ and the maximum conductance of Ca2+ -dependent cationic current as well as the intensity of input current systematically control the bursting mode, these quantities may be crucial for the regulation of the coherence of local cortical activity. Numerical simulations demonstrate that the modulations of the calcium sensitivity and the amplitude of the cationic current can induce rapid transitions between synchrony and asynchrony in a large-scale network of chattering neurons. The rapid synchronization of chattering neurons is shown to synchronize the activities of regular spiking pyramidal neurons at the gamma frequencies, as may be necessary for selective attention or binding processing in object recognition.
Rozprawy doktorskie na temat "Oscillation mode transition"
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Banerjee, Sayanti P. "A Mathematical Model for the Transition in Firing Patterns Across Puberty of a Gonadotropin-Releasing Hormone Neuron". The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1357249691.
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Agrawal, Devanshu. "A Numerical Model for Nonadiabatic Transitions in Molecules". Digital Commons @ East Tennessee State University, 2014. https://dc.etsu.edu/honors/193.
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In molecules, electronic state transitions can occur via quantum coupling of the states. If the coupling is due to the kinetic energy of the molecular nuclei, then electronic transitions are best represented in the adiabatic frame. If the coupling is instead facilitated through the potential energy of the nuclei, then electronic transitions are better represented in the diabatic frame. In our study, we modeled these latter transitions, called ``nonadiabatic transitions.'' For one nuclear degree of freedom, we modeled the de-excitation of a diatomic molecule. For two nuclear degrees of freedom, we modeled the de-excitation of an ethane-like molecule undergoing cis-trans isomerization. For both cases, we studied the dependence of the de-excitation on the nuclear configuration and potential energy of the molecule.
We constructed a numerical model to solve the time-dependent Schr\"{o}dinger Equation for two coupled wave functions. Our algorithm takes full advantage of the sparseness of the numerical system, leading to a final set of equations that is solved recursively using nothing more than the Tridiagonal Algorithm.
We observed that the most effective de-excitation occurred when the molecule transitioned from a stable equilibrium configuration to an unstable equilibrium configuration. This same mechanism is known to drive fast electronic transitions in the adiabatic frame. We concluded that while the adiabatic and diabatic frames are strongly opposed physically, the mathematical mechanism driving electronic transitions in the two frames is in some sense the same.
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Petrolli, Vanni. "Confinement induced transition between wave-like cellular migration modes". Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY056.
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La capacité des cellules à générer spontanément de l'ordre a l’échelle supra cellulaire repose sur l'interaction de signaux mécaniques et biochimiques. Si le consensus général est que la signalisation chimique est le régulateur principal du comportement cellulaire, il est aujourd’hui bien établi que l'impact des facteurs mécaniques est primordial sur des processus fondamentaux de la physiologie cellulaire tel que la différenciation, la prolifération, la motilité et qu’une dérégulation des paramètres mécaniques du microenvironnement des cellules sont impliqués dans un grand nombre de pathologies allant du cancer aux myopathies. Dans ce contexte, plusieurs études ont récemment mis en évidence l'existence d’ondes mécaniques se propageant à l’échelle supra-cellulaire.Nous étudions dans le cadre de cette thèse l'origine de ces ondes de vitesse dans les tissus et discutons leur origine biologique. En pratique, nous confinons des monocouches de cellules épithéliales à des géométries quasi unidimensionnelles, pour forcer l'établissement presque omniprésent d'ondes au niveau tissulaire. En accordant la longueur des tissus, nous découvrons l'existence d'une transition de phase entre les oscillations globales et multi-nodales, et prouvons que dans ce dernier régime, longueur d'onde et période sont indépendantes de la longueur de confinement. Ces résultats démontrent que l’origine de ces oscillations est intrinsèque au système biologique, ce mécanisme apparait comme un candidat pertinent permettant aux cellules de mesurer avec précision des distances au niveau supra-cellulaire et potentiellement de structurer spatialement un tissu. Des simulations numériques basées sur un modèle de type Self-propelled Voronoi reproduisent la transition de phase que nous avons observé expérimentalement et aident à guider nos recherches sur l'origine de ces phénomènes ondulatoires et leur rôle potentiel dans l'apparition spontanée des follicules pileux dans les explants cutanés des sourisThe ability of organisms to spontaneously generate order relies on the intricate interplay of mechanical and bio-chemical signals. If the general consensus is that chemical signaling governs the behavior of cells, an increasing amount of evidence points towards the impact of mechanical factors into differentiation, proliferation, motility and cancer progression. In this context, several studies recently highlighted the existence of long-range mechanical excitations (i.e. waves) at the supra-cellular level.Here, we investigate the origins of those velocity waves in tissues and their correlation with the presence of boundaries. Practically, we confine epithelial cell mono-layers to quasi-one dimensional geometries, to force the almost ubiquitous establishment of tissue-level waves. By tuning the length of the tissues, we uncover the existence of a phase transition between global and multi-nodal oscillations, and prove that in the latter regime, wavelength and period are independent of the confinement length. Together, these results demonstrate the intrinsic origin of tissue oscillations, which could provide cells with a mechanism to accurately measure distances at the supra-cellular level and ultimately lead to spatial patterning. Numerical simulations based on a Self-propelled Voronoi model reproduce the phase transition we measured experimentally and help in guiding our preliminary investigations on the origin of these wave-like phenomena, and their potential role for the spontaneous appearance of hair follicles in mouse skin explants
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PIMENTA, MARCOS ASSUNCAO. "Transitions de phase a haute temperature et conduction ionique dans likso:(4) et composes apparentes". Orléans, 1987. http://www.theses.fr/1987ORLE2045.
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Etude par reflexion ir, diffusion brillouin et la mesure des conductivites electriques sur likso::(4), linaso::(4) et linh::(4)so::(4). Identification et analyse des differentes transitions; mise en evidence d'une relation etroite entre la mobilite cationique et les mouvements de rotationd es groupes sulfate. Observation d'une transition ordre-desordre a 435**(o)c, avec phse intermediaire a surstructure de basse symetrie, dans le cas de likso::(4)
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Collura, Mario. "Aspects hors de l'équilibre de systèmes quantiques unidimensionnels fortement corrélés". Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0009/document.
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Dans cette thèse, nous avons répondu à certaines questions ouverts dans le domaine de la dynamique hors équilibre des systèmes quantiques unidimensionnels fermés. Durant ces dernières années, les avancées dans les techniques expérimentales ont revitalisé la recherche théorique en physique de la matière condensée et dans l'optique quantique. Nous avons traité trois sujets différents et en utilisant des techniques à la fois numériques et analytiques. Dans le cadre des techniques numériques, nous avons utilisé des méthodes de diagonalisation exacte, l'algorithme du groupe de renormalisation de la matrice densité en fonction du temps (t-DMRG) et l'algorithme de Lanczos. Au début, nous avons étudié la dynamique quantique adiabatique d'un système quantique près d'un point critique. Nous avons démontré que la présence d'un potentiel de confinement modifie fortement les propriétés d'échelle de la dynamique des observables en proximité du point critique quantique. La densité d'excitations moyenne et l'excès d'énergie, après le croisement du point critique, suivent une loi algébrique en fonction de la vitesse de la trempe avec un exposant qui dépend des propriétés spatio-temporelles du potentiel. Ensuite, nous avons étudié le comportement de bosons ultra-froids dans un réseau optique incliné. En commençant par l'hamiltonien de Bose-Hubbard, dans la limite de Hard-Core bosons, nous avons développé une théorie hydrodynamique qui reproduit exactement l'évolution temporelle d'une partie des observables du système. En particulier, nous avons observé qu'une partie de bosons reste piégée, et oscille avec une fréquence qui dépend de la pente du potentiel, au contraire, une autre partie est expulsée hors de la rampe. Nous avons également analysé la dynamique du modèle de Bose-Hubbard en utilisant l'algorithme t-DMRG et l'algorithme de Lanczos. De cette façon, nous avons mis en évidence le rôle de la non-intégrabilité du modèle dans son comportement dynamique. Enfin, nous avons abordé le problème de la thermalisation dans un système quantique étendu. À partir de considérations générales, nous avons introduit la notion de profil de température hors équilibre dans une chaîne des bosons à coeur dure. Nous avons analysé la dynamique du profil de temperature et, notamment, ses propriétés d'échelleIn this thesis we have addressed some open questions on the out-of-equilibrium dynamics of closed one-dimensional quantum systems. In recent years, advances in experimental techniques have revitalized the theoretical research in condensed matter physics and quantum optics. We have treated three different subjects using both numerical and analytical techniques. As far as the numerical techniques are concerned, we have used essentially exact diagonalization methods, the adaptive time-dependent density-matrix renormalization-group algorithm (t-DMRG) and the Lanczos algorithm. At first, we studied the adiabatic quantum dynamics of a quantum system close to a critical point. We have demonstrated that the presence of a confining potential strongly affects the scaling properties of the dynamical observables near the quantum critical point. The mean excitation density and the energy excess, after the crossing of the critical point, follow an algebraic law as a function of the sweeping rate with an exponent that depends on the space-time properties of the potential. After that, we have studied the behavior of ultra-cold bosons in a tilted optical lattice. Starting with the Bose-Hubbard Hamiltonian, in the limit of Hard-Core bosons, we have developed a hydrodynamic theory that exactly reproduces the temporal evolution of some of the observables of the system. In particular, it was observed that part of the boson density remains trapped, and oscillates with a frequency that depends on the slope of the potential, whereas the remaining packet part is expelled out of the ramp. We have also analyzed the dynamics of the Bose-Hubbard model using the tDMRG algorithm and the Lanczos algorithm. In this way we have highlighted the role of the non-integrability of the model on its dynamical behavior. Finally, we have addressed the issue of thermalization in an extended quantum system. Starting from quite general considerations, we have introduced the notion of out-of-equilibrium temperature profile in a chain of Hard-Core bosons. We have analyzed the dynamics of the temperature profile and especially its scaling properties
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Juan, Yen-Chia, i 阮彥嘉. "Study of the Asynchronous Harmonic Mode-locking and FM Oscillation Transition in a 10 GHz Hybrid Mode-locked Er-doped Fiber Laser". Thesis, 2018. http://ndltd.ncl.edu.tw/handle/j8gsyv.
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碩士國立交通大學
光電工程研究所
107
In this thesis, we successfully demonstrate the asynchronous harmonic mode-locking and frequency modulation (FM) oscillation transition with increasing detuning frequencies in a 10 GHz hybrid mode-locked Er-doped fiber laser. We also simulate the states of lasing under different detuning frequencies as well as the external pulse compression results under the FM oscillation state. The experimental and simulation results are in good agreement.
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Chatterjee, Banhi. "Screening and Friedel oscillations in inhomogeneous systems with correlated fermions". Doctoral thesis, 2016. https://depotuw.ceon.pl/handle/item/2008.
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The thesis presents theoretical and numerical studies on electronic screening and Friedel
Oscillations (FO) in correlated fermionic systems in the presence of external
inhomogeneity. These spatial oscillations in the electronic densities appear in the
neighbourhood of the impurity due to quantum scattering from the impurity. They are
observed in metals at low temperatures. The interacting system has been modeled by
the Hubbard Hamiltonian which has been further solved numerically using the Real
space Dynamical Mean-Field Theory (R-DMFT). We study one-, two-, and three-
dimensional finite lattice systems with periodic boundary conditions. The
inhomogeneous potential has been modeled by a single impurity, two impurities and an
extended inhomogeneity. Different approximations accounting for the electronic
correlations have also been discussed in the course of the thesis. The effects of electronic
correlations, particularly at the Mott metal to insulator transition, on the behaviour of FO
have been explored. According to our numerical studies, the oscillations are damped
with the interactions, disappear at the Mott transition and completely beyond it. At finite
temperature the oscillations are damped and slowly disappear as we increase the
temperature of the system. At half-filling the period and phase of the oscillations remain
unaltered by the interactions. The Friedel sum rule for the interacting system has been
investigated. The variation of the screening charge around the neighbourhood of the
impurity called ``Neighbourhood screening charge'' or ``N-screening charge'' with
interaction, temperature is studied for different impurity potentials. It is further seen that
the interactions weaken the screening effects. The spectral functions in the presence of
an external inhomogeneity and electronic interactions have been studied at different
lattice sites. In the presence of the interaction a sign of resonance appears in the spectral
function at the impurity site. In the presence of two impurities interaction weakens the
interference effects on the oscillations. Finally the one-body scattering formalism is
modified to describe analytically the effects of correlations in many body systems
modeled by a momentum independent self-energy with semi circular density of states.
Effects of electronic correlations in the scattering phase-shift and spectral functions are
obtained in our calculations. The thesis provides predictive numerical results which can
motivate future experiments.Rozprawa doktorska zawiera analizę teoretyczną oraz obliczenia numeryczne dotyczące ekranowania elektronowego oraz oscylacji Friedel'a (FO) w silnie skorelowanych układach fermionowych w obecności niejednorodnego potencjału zewnętrznego. Przestrzenne oscylacje gęstości elektronowej pojawiają się w sąsiedztwie domieszki na skutek kwantowego rozpraszania na domieszce. Oscylacje te obserwuje się w niskich temperaturach w układach metalicznych. Układ oddziałujący modelowany jest w rozprawie za pomocą hamiltonianu Hubbarda, który został rozwiązany numerycznie w przybliżeniu dynamicznej teorii pola średniego w zastosowaniu do układu niejednorodnego przestrzennie (RDMFT). Rozważane są jedno, dwu i trójwymiarowe układy sieciowe z periodycznymi warunkami brzegowymi. Zewnętrzny potencjał niejednorodny modelowany jest za pomocą pojedynczej domieszki, dwóch domieszek lub niejednorodności obejmującej większą liczbę węzłów sieci. W rozprawie rozważane są różne modele uwzględniające oddziaływania elektronowe. Badano efekty tych oddziaływań na oscylacje Friedla, w szczególności blisko przejścia Motta metal-izolator. Wyniki obliczeń numerycznych zaprezentowanych w rozprawie pokazują, że oscylacje Friedla są tłumione przez oddziaływania elektronowe, zanikają wokół przejścia Motta i są całkowicie wygaszone w fazie izolatora. Wzrost temperatury układu powoduje tłumienie oscylacji. Okres i faza oscylacji nie zależą od wielkości oddziaływań, gdy gęstość cząstek odpowiada sytuacji w której pasmo jest w połowie zapełnienie. W rozprawie badano również spełnienie reguły sum Friedla w przypadku układów oddziałujących. Ponadto badano zmianę ładunku ekranującego wokół domieszki określaną jako ładunek ekranowania wokół domieszki (ang. "Neighbour screening charge" lub "N-screening charge") w zależności od oddziaływania, temperatury i dla różnych wartości potencjałów na domieszce. Badania w rozprawie pokazują, że oddziaływania osłabiają efekty ekranowania. Przedstawiono funkcje spektralne w obecności zewnętrznej niejednorodności i oddziaływań elektronowych na różnych węzłach sieci. W obecności dwóch domieszek oddziaływania osłabiają wpływ efektów interferencyjnych domieszek na oscylacje. Formalizm rozpraszania jednociałowego zmodyfikowano w celu opisu efektów korelacji w wielociałowych układach poprzez wprowadzenie energii własnej niezależnej od pędu odpowiadającej eliptycznej gęstości stanów. Rezultaty obliczeń uwidaczniają wpływ korelacji elektronowych na przesunięcie fazowe i funkcję spektralną. Rozprawa zawiera rezultaty numeryczne, które mogą stanowić motywację do przyszłych badań eksperymentalnych.
Książki na temat "Oscillation mode transition"
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Bauer, Christopher. Low Reynolds number [kappa]-[epsilon] and empirical transition models for oscillatory pipe flow and heat transfer. [Washington, D.C: National Aeronautics and Space Administration, 1993.
Znajdź pełny tekst źródłaCzęści książek na temat "Oscillation mode transition"
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Dana, Syamal Kumar, i Satyabrata Chakraborty. "Experimental Evidences of Shil'nikov Chaos and Mixed-mode Oscillation in Chua Circuit". W Chaos Synchronization and Cryptography for Secure Communications, 91–104. IGI Global, 2011. http://dx.doi.org/10.4018/978-1-61520-737-4.ch005.
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Experimental evidences of Shil’nikov type homoclinic chaos and mixed mode oscillations are presented in asymmetry-induced Chua‘s oscillator. The asymmetry plays a crucial role in the related homoclinic bifurcations. The asymmetry is introduced in the circuit by forcing a DC voltage. The authors observed transition from large amplitude limit cycle to homoclinic chaos via a sequence of mixed-mode oscillations interspersed by chaotic states by tuning a control parameter.
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Kotkin, Gleb L., i Valeriy G. Serbo. "Non-linear oscillations". W Exploring Classical Mechanics, 45–47. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780198853787.003.0008.
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This chapter addresses the distortion in the free and forced oscillations of a harmonic oscillator caused by the presence of the anharmonic terms in the potential energy, a simple model related to the coupling of the longitudinal and flexural oscillations inmolecules, and two oscillators with a weak non-linear coupling (the so-called Fermi resonance). The chapter also examines non-linear resonances, the parametric resonances, drift of the orbit centre for a charged particle in the weakly inhomogeneous magnetic field, and a mechanical model of phase transitions of the second kind.
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Kotkin, Gleb L., i Valeriy G. Serbo. "Non-linear oscillations". W Exploring Classical Mechanics, 265–78. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780198853787.003.0021.
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This chapter addresses the distortion in the free and forced oscillations of a harmonic oscillator caused by the presence of the anharmonic terms in the potential energy, a simple model related to the coupling of the longitudinal and flexural oscillations inmolecules, and two oscillators with a weak non-linear coupling (the so-called Fermi resonance). The chapter also examines non-linear resonances, the parametric resonances, drift of the orbit centre for a charged particle in the weakly inhomogeneous magnetic field, and a mechanical model of phase transitions of the second kind.
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Saputra, Azhar Aulia, i Naoyuki Kubota. "A Multi-Objective Evolutionary Algorithm for Neuro-Locomotion of a Legged Robot With Malfunction Compensation". W Global Perspectives on Robotics and Autonomous Systems, 1–23. IGI Global, 2023. http://dx.doi.org/10.4018/978-1-6684-7791-5.ch001.
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Dynamic quadruped locomotion implies high-intensity integration toward environmental factors and requires considering the information from sensory feedback. The authors represent CPG-based locomotion model with sensorimotor coordination. They build an efficient integration between motor and sensory neurons that can generate dynamic behavior, especially in locomotion coordination during leg malfunction. They emphasize an optimization strategy to optimize the interconnection structure of CPG-based locomotion model. They use a multi-objective evolutionary algorithm to optimize the synaptic weight between motor–motor neurons and motor–sensory neurons. The applied cascade optimization is 1) dynamic gait pattern optimization using desired speed and torso oscillation as the fitness function and 2) malfunction compensation optimization using moving direction error and torso oscillation as the fitness evaluation. The proposed model has been applied to simulated and real middle-size quadruped robots. It showed the proposed optimization can generate a smooth transition during a robot's leg unction.
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Nitzan, Abraham. "The Spin–Boson Model". W Chemical Dynamics in Condensed Phases. Oxford University Press, 2006. http://dx.doi.org/10.1093/oso/9780198529798.003.0018.
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In a generic quantum mechanical description of a molecule interacting with its thermal environment, the molecule is represented as a few level system (in the simplest description just two, for example, ground and excited states) and the environment is often modeled as a bath of harmonic oscillators. The resulting theoretical framework is known as the spin–boson model, a term that seems to have emerged in the Kondo problem literature (which deals with the behavior of magnetic impurities in metals) during the 1960s, but is now used in a much broader context. Indeed, it has become one of the central models of theoretical physics, with applications in physics, chemistry, and biology that range far beyond the subject of this book. Transitions between molecular electronic states coupled to nuclear vibrations, environmental phonons, and photon modes of the radiation field fall within this class of problems. The present chapter discusses this model and some of its mathematical implications. The reader may note that some of the subjects discussed in Chapter 9 are reiterated here in this more general framework. In Sections 2.2 and 2.9 we have discussed the dynamics of the two-level system and of the harmonic oscillator, respectively. These exactly soluble models are often used as prototypes of important classes of physical system. The harmonic oscillator is an exact model for a mode of the radiation field and provides good starting points for describing nuclear motions in molecules and in solid environments. It can also describe the short-time dynamics of liquid environments via the instantaneous normal mode approach. In fact, many linear response treatments in both classical and quantum dynamics lead to harmonic oscillator models: Linear response implies that forces responsible for the return of a system to equilibrium depend linearly on the deviation from equilibrium—a harmonic oscillator property! We will see a specific example of this phenomenology in our discussion of dielectric response in Section 16.9.
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Ma, Suqi. "Dynamics of a Neutrophil Model with State Feedback Control of Time Delay". W Bifurcation Theory and Applications [Working Title]. IntechOpen, 2023. http://dx.doi.org/10.5772/intechopen.111750.
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The complex periodical transition phenomena of the neutrophil model are investigated underlying delay feedback control strategy. By application of DDE-Biftool software, which develops an artificial technique to compute codimension 1 bifurcation of periodical solutions with singularity, both of the route of P-2 solutions to homoclinic bifurcation and the period-doubling bifurcation phenomena are investigated. The Bautin bifurcation point departs the subcritical Hopf point from the supercritical Hopf point. The Bautin point observed within the first Hopf point is the intersection point of the Hopf line with the limit point cycle bifurcation line; however, the Bautin point discovered with the second Hopf point is distinct via a special scheme as the lineup of periodical solution circle broken. The numerical simulation results aid to provide a helpful understanding in periodical oscillation phenomena of the neutrophil model.
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Cañete Mesa, Rafael. "Phasic Structure of the Standard Model". W Redefining Standard Model Particle Physics [Working Title]. IntechOpen, 2023. http://dx.doi.org/10.5772/intechopen.109384.
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We present a physical relationship able to justify by itself the whole spectrum of fundamental particles of matter (fermions), that is, the hierarchical structure, the value of their masses, the basis of those values and the analytical and positional relation of the same. A hierarchy supported on an element of periodicity or sequence of differentiated states (phases) that makes it resemble a periodic table of elementary particles, which allows us to define material states not well defined until now and others unregistered, with which it is precisely evidenced that there has to exist a particle M=171.87eV, or an equivalent energy entity, which represents a common zero generation to (anti)quarks and charged (anti)leptons, as well as a mediator particle in the connection of these with (anti)neutrinos, for which, by applying this methodology, we obtain a massive base ν1,ν2,ν3, consistent with the theoretical and experimental requirements for neutrino oscillation, which allows us to explain the CP violation. Previously, we obtained, by means of the quantum wave formulation, a symmetrized wave packet (SWP) and an associated energy transmutation equation, equivalent, although more general and precise, to the one obtained by means of a corpuscular treatment, this one that we will use and accounts for all the transitions between particles.
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Roguai, Sabrina, i Abdelkader Djelloul. "Roles of Cobalt Doping on Structural and Optical of ZnO Thin Films by Ultrasonic Spray Pyrolysis". W Thin Films [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.95920.
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Here we report a systematic study of structural, optical, and magnetic measurements of Zn1-xCoxO (x = 0–0.22 at.%) by Ultrasound pyrolysis spray technique. The hexagonal wurtzite structure of our films is confirmed by X-ray diffraction with an average crystallite size estimated in the range of 18–30 nm. For the optical proprieties, using the Levenberg–Marquardt least squares rule, the experimental transmission measurements were perfectly adapted to the transmission data calculated by a combination of the Wemple-DiDomenico model, the absorption coefficient of an electronic transition and the Tauc-Urbach model. The concentration of the NCo absorption centers and the oscillator intensity f of the d-d transition of Co2+ ions are determined by the Smakula method. The presence of high concentrations of localized states in the thin films is responsible for the reduction in the width of optical bandgap.
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Reyes, Tiffany, i Bo-Wen Shen. "A Recurrence Analysis of Multiple African Easterly Waves during Summer 2006". W Current Topics in Tropical Cyclone Research. IntechOpen, 2020. http://dx.doi.org/10.5772/intechopen.86859.
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Accurate detection of large-scale atmospheric tropical waves, such as African easterly waves (AEWs), may help extend lead times for predicting tropical cyclone (TC) genesis. Since observed AEWs have comparable but slightly different periods showing spatial and temporal variations, local analysis of frequencies and amplitudes of AEWs is crucial for revealing the role of AEWs in the modulation of TC genesis. To achieve this goal, we investigate the recurrence plot (RP) method. A recurrence is defined when the trajectory of a state returns to the neighborhood of a previously visited state. To verify implementation of the RP method in Python and its capability for revealing a transition between different types of solutions, we apply the RP to analyze several idealized solutions, including periodic, quasiperiodic, chaotic and limit cycle solutions, and various types of solutions within the three- and five-dimensional Lorenz models. We then extend the RP analysis to two datasets from the European Centre for Medium-Range Weather Forecasts global reanalysis and global mesoscale model data in order to reveal the recurrence of multiple AEWs during summer 2006. Our results indicate that the RP analysis effectively displays the major features of time-varying oscillations and the growing or decaying amplitudes of multiple AEWs.
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Thomas, Michael E. "Spectroscopy of Matter". W Optical Propagation in Linear Media. Oxford University Press, 2006. http://dx.doi.org/10.1093/oso/9780195091618.003.0007.
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It is critical to understand the nature of the propagation medium in terms of the available resonances which couple to the electromagnetic field. The detailed specification of the complex index of refraction as a function of frequency is the subject of spectroscopy. Since propagation media cover all phases of matter, the spectroscopy of gases, solids, and liquids is introduced in this chapter. Topics are not exhaustively covered, but rather with sufficient depth to support the practical applications that will come later. The chapter begins with a formal review of topics covered in stationary-state quantum mechanics necessary for the development of spectroscopy. The next section develops models to calculate spectral line positions, which are necessary to characterize a spectral line. The full development of spectral line parameters is not only the goal of this chapter but the next two as well. The remaining sections address the essential elements of the spectroscopy of gases, solids and liquids. Both classical and quantum models are used. Time-independent quantum mechanics allows the description of the quantized energy level structure of matter. This is the central topic of this chapter. Time-dependent quantum mechanics is necessary for the development of a theory covering transitions between stationary-state energy levels and is the topic of Chapter 5. The classical concept of light is that of an oscillating continuous wave field, as presented in the first two chapters. This is consistent with the classical electrodynamics based on Maxwell’s equations. However, the work by Planck on blackbody radiation and Einstein on the photoelectric effect showed that optical fields also have a quantized or particle-like nature. Planck, in 1900, suggested that the energy of light, E, be quantized according to . . . E = h f [J] (3.1) . . . where f is frequency (sec−1) and h is Planck’s constant (h = 6.6260755(40) × 10−34 J-sec). This allowed a theoretical description of blackbody radiation for the first time. However, it was Einstein, who, a few years later, made Eq. 3.1 more credible by applying it to explain the photoelectric effect.
Streszczenia konferencji na temat "Oscillation mode transition"
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Hara, Kentaro, Iain D. Boyd, Michael J. Sekerak i Alec D. Gallimore. "Discharge oscillation mode transition of a Hall thruster". W 2014 IEEE 41st International Conference on Plasma Sciences (ICOPS) held with 2014 IEEE International Conference on High-Power Particle Beams (BEAMS). IEEE, 2014. http://dx.doi.org/10.1109/plasma.2014.7012518.
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Sekerak, Michael J., Benjamin W. Longmier i Alec D. Gallimore. "Mode transition characteristics and oscillation frequencies in Hall Effect Thrusters". W 2014 IEEE 41st International Conference on Plasma Sciences (ICOPS) held with 2014 IEEE International Conference on High-Power Particle Beams (BEAMS). IEEE, 2014. http://dx.doi.org/10.1109/plasma.2014.7012517.
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Luo, Cheng-Jhih, Yen-Chia Juan i Yinchieh Lai. "Asynchronous mode-locking and FM oscillation transition in a 10 GHz hybrid mode-locked fiber laser". W Conference on Lasers and Electro-Optics/Pacific Rim. Washington, D.C.: OSA, 2018. http://dx.doi.org/10.1364/cleopr.2018.tu2b.3.
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Pan, Deng, Tong Zhu i Chenzhen Ji. "INVESTIGATIONS ON THE EFFECTS OF FLUE GAS RECIRCULATION ON THE COMBUSTION INSTABILITY OF A PREMIXED FLAME FOR THE LOW NOX EMISSIONS". W GPPS Xi'an21. GPPS, 2022. http://dx.doi.org/10.33737/gpps21-tc-347.
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The combustion instability has been a common problem accompany with the low NOx emission technologies in industrial premixed burner. The effects of flue gas recirculation ratio (FR) on the characteristics of combustion instability and NOx emissions of an industrial scale premixed burner were investigated with experiments and numerical simulation. The acoustic mode of the whole chamber was computed with a Helmholtz solver combined with CFD simulation. The NOx emissions significantly decrease with the increasing of the FR. As FR increases from 0% to 20% the NOx emission reduces about 85%. Four modes of pressure oscillations in the combustion chamber with different FRs were found in the experiment. The pressure oscillation exhibits combustion noise mode at low FRs (<10%) in which conditions the pressure oscillation amplitude is low and there is no distinct frequency. Two dominant pressure oscillation frequency ranging from 21Hz to 25Hz and ranging from 1Hz to 2Hz are observed under relatively high FRs. The first acoustic mode frequency is 5.3Hz~5.7Hz and the second acoustic mode frequency is 23.1Hz~24.1Hz which are close to the pressure oscillation frequencies observed in the experiment. The ultra-low frequency and high amplitude pressure oscillations are attributed the periodic overall extinguish and ignition of the flame under high FRs. The difference between the pressure oscillation frequencies and the acoustic cavity mode frequencies may be attributed to the interaction of the response of the flame and the cavity acoustic mode which can lead to mode transition.
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Ueno, Ichiro, Keishi Matsumoto, Atsumi Machida i Tsuyoshi Hanyu. "Shape Oscillation of Bubble(s) in Acoustic Field". W 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22636.
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We focus on dynamics of multiple air bubbles exposed to acoustic pressure field while ascending in water. The bubbles are injected into the pool filled with water from a vertical capillary tube, and then the acoustic wave of designated frequency is applied toward the bubbles. The frequency of the acoustic wave is varied from 0.5 to 20 kHz. Volume and shape oscillations of the bubbles are captured by a high-speed camera at frame rates up to 40000 fps with a back-lighting system. Through this system, we succeed in capturing the dynamics of the axisymmetric shape oscillation with a distinct mode number; the bubble exhibits the volume oscillation first with a fundamental frequency f0, and then the gradual transition to the shape oscillation with a fundamental frequency fnm takes place. We evaluate the correlation through the careful observations between the f0 and fnm as f0 ∼ 2.1fnm, which brings almost perfectly confirmation of the prediction through the preceding theoretical works. We also indicate the criterion of the excitation of the shape oscillation by varying the frequencies of the adding pressure field.
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Kawai, Hideki, Tomoki Honma i Hiroshige Kikura. "Spectrum Analysis of the Taylor Vortex Flow With a Short Annulus Using the Ultrasonic Velocity Profiler". W ASME-JSME-KSME 2011 Joint Fluids Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajk2011-11026.
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Mild mixing effect is observed in the Taylor vortex flow (TVF) system in which the animal and plant cell walls are not disrupted as much as other bioreactor systems. These facts would be more important in developing a new bioreactor system, which plays an active role in the medical and bioindustrial fields. Although the mixing methods with an impeller are often used for an agitation in synthetic polymerization, the problem is that there exists a high shearing flow region just after the moving impeller. This region for instance, would cause the destruction of the alga cell when a microorganism in suspension is used as a bioreactor. The TVF is expected to reduce the local increase of these shearing forces because the device doesn’t have any impeller, and lead the bioreactor system to more uniform and stable states in the flow fields for cultivation or oxygen production. TVF in a single-phase flow with an infinite annulus is well known since it has a spectrum transition to turbulence and the oscillation is observed from the wavy vortex mode. Recent Takeda’s study has measured the precise spatiotemporal velocity fields by using the ultrasonic velocity profiler (UVP). On the other hand with a short annulus, we have various vortex modes generated due to the Ekman boundary layers occurred near the upper and lower solid boundaries. Each vortex mode also has the same spectrum transition such as wavy, modulated and soft turbulence modes. But the flow state seems much different from the infinite annulus. Present study measures the velocity profiles of the flow in TVF with a short annulus by using the UVP. We focus on not only the velocity profiles, but also the spectra in oscillation mode that occurs in different vortex modes. From the results, the spectra of the various oscillations are occurred with increase of Reynolds number, and seem different from those in the infinite annulus. This oscillation analysis would contribute to the basic knowledge of the mixing effect in solid-liquid flow when a microorganism in suspension is used as a bioreactor.
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Rhee, J. K., T. B. Norris, Y. Arakawa, M. Nishioka i C. Weisbuch. "Dynamics of Coherently Excited Semiconductor Microcavities". W International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 1994. http://dx.doi.org/10.1364/up.1994.tue.5.
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Recently, cavity quantum electrodynamic (QED) effects in semiconductor microcavities have been of considerable interest since, in the weak-coupling regime they play an important role in selectively increasing spontaneous emission into the lasing mode of vertical-cavity surface-emitting lasers (VCSEL’s) [1,2], enabling low-threshold, high speed, and high efficiency. In a strong-coupling regime, the normal modes of the coupled system are superpositions of the exciton and cavity modes. Hence the impulsively excited system will evolve in time with the energy oscillating between the exciton and cavity modes. This is known as a vacuum-Rabi oscillation (VRO), with a frequency of Ω=d¯⋅E¯/@@h, where d¯ is the transition dipole moment of atoms and E¯ the vacuum-field strength. Of course, VRO are observable only when the cavity lifetime and exciton dephasing time are long enough compared to VRO period. Recently, Weisbuch et al. [3] have reported an observation of the normal-mode vacuum Rabi splitting in 2-D-exciton/planar-DBR microcavities. The observed splittings were as large as 6 meV in reflection and transmission spectra, implying 690-fs vacuum Rabi oscillations.
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Milonni, P. W., i Mei-Li Shih. "Instabilities and Chaos in Multimode Homogeneously Broadened Lasers". W Instabilities and Dynamics of Lasers and Nonlinear Optical Systems. Washington, D.C.: Optica Publishing Group, 1985. http://dx.doi.org/10.1364/idlnos.1985.tha2.
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The experiments of Hillman, et al. [1] with a ring dye laser indicate that single-mode homogeneously broadened oscillation is intrinsically unstable at high pumping levels. Motivated by this work, we have considered various formulations of the general multimode problem. We find that certain aspects of these experiments, such as the transition from single to multimode oscillation with increased pumping, can be understood within the thin-sheet gain model in which spatial hole burning is completely ignored. (We hope by the time of our presentation to be more precise about the comparison of theory and experiment.) Following the bifurcation of the single-mode steady state and the onset of two modes symmetrically displaced about line center, there is a period-doubling route to chaos which is not evident in the experiments thus far. The familiar "gain clamping" assumption of single-mode oscillation in a homogeneously broadened laser is incorrect at high pumping levels, even in the absence of spatial hole burning. Our results appear to be consistent with the arguments advanced by Hillman, et al. on the basis of a model in which the atoms are driven by the field but do not react back on it.
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Fan, T. Y., i Robert L. Byer. "Continuous-wave room-temperature Nd:YAG laser at 946 nm". W OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1986. http://dx.doi.org/10.1364/oam.1986.fk4.
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Nd-doped solid-state lasers have been demonstrated in the wavelength region centered about 940 nm, the 4F3/2—4l9/2 transition. Typically it is difficult to achieve oscillation on this transition because the lower laser manifold is also the ground state manifold, and the gain near 1.05 μm; the 4F3/2—4l11/2 transition is higher. The first causes the threshold to be higher because the lower laser level is populated, and the second causes difficulties because of parasitic oscillation of the 4F3/2—4l11/2 transition. However, these difficulties can be overcome; we have demonstrated cw oscillation at 946 nm at room temperature with a threshold of 11 mW of absorbed pump power at 588 nm in Nd:YAG. The slope efficiency is only 3.6%, but the nominal output coupling of 0.3% is below optimum. By cooling the laser from 296 to 256 K, which reduces the lower laser level population, the threshold was reduced to 7 mW. The pump beam was chopped for all these quantitative measurements to reduce effects of heating of the crystal, but true cw oscillation was also demonstrated. While this threshold power is low, further reduction of threshold appears possible by optimization of the cavity mode volume.
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Sampath, Ramgopal, i S. R. Chakravarthy. "Effect of Acoustic Feedback on Lagrangian Coherent Structures in a Backward Facing Step Combustor With a Partially Premixed Flame". W ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/gt2017-64856.
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The thermoacoustic oscillations of a partially premixed flame stabilized in a backward facing step combustor are studied at a constant equivalence ratio in long and short combustor configurations corresponding to with and without acoustic feedback respectively. We perform simultaneous time-resolved particle image velocimetry (TR-PIV) and chemiluminescence for selected flow conditions based on the acoustic characterization in the long combustor. The acoustic characterization shows a transition in the dominant pressure amplitudes from low to high magnitudes with an increase in the inlet flow Reynolds number. This is accompanied by a shift in the dominant frequencies. For the intermittent pressure oscillations in the long combustor, the wavelet analysis indicates a switch between the acoustic and vortex modes with silent zones of relatively low-pressure amplitudes. The short combustor configuration indicates the presence of the vortex shedding frequency and an additional band comprising the Kelvin Helmholtz mode. Next, we apply the method of finite-time Lyapunov exponent (FTLE) to the time-resolved velocity fields to extract features of the Lagrangian coherent structures (LCS) of the flow. In the long combustor post transition with the time instants with dominant acoustic mode, a large-scale modulation of the FTLE boundaries over one cycle of pressure oscillation is evident. Further, the FTLEs and the flame boundaries align each other for all phases of the pressure oscillation. In the short combustor, the FTLEs indicate the presence of small wavelength waviness that overrides the large-scale vortex structure, which corresponds to the vortex shedding mode. This behaviour contrasts with the premixed flame in the short combustor reported earlier in which such large scales were found to be seldom present. The presence of the large-scale structures even in the absence of acoustic feedback in a partially premixed flame signifies its inherent unstable nature leading to large pressure amplitudes during acoustic feedback. Lastly, the FTLE boundaries provide the frequency information of the identified coherent structure and also acts as the surrogate flame boundaries that are estimated from just the velocity fields.
Raporty organizacyjne na temat "Oscillation mode transition"
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Wagner, D. Ry, Eliezer Lifschitz i Steve A. Kay. Molecular Genetic Analysis of Flowering in Arabidopsis and Tomato. United States Department of Agriculture, maj 2002. http://dx.doi.org/10.32747/2002.7585198.bard.
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The primary objectives for the US lab included: the characterization of ELF3 transcription and translation; the creation and characterization of various transgenic lines that misexpress ELF3; defining genetic pathways related to ELF3 function regulating floral initiation in Arabidopsis; and the identification of genes that either interact with or are regulated by ELF3. Light quality, photoperiod, and temperature often act as important and, for some species, essential environmental cues for the initiation of flowering. However, there is relatively little information on the molecular mechanisms that directly regulate the developmental pathway from the reception of the inductive light signals to the onset of flowering and the initiation of floral meristems. The ELF3 gene was identified as possibly having a role in light-mediated floral regulation since elj3 mutants not only flower early, but exhibit light-dependent circadian defects. We began investigating ELF3's role in light signalling and flowering by cloning the ELF3 gene. ELF3 is a novel gene only present in plant species; however, there is an ELF3 homolog within Arabidopsis. The Arabidopsis elj3 mutation causes arrhythmic circadian output in continuous light; however, we show conclusively normal circadian function with no alteration of period length in elj3 mutants in dark conditions and that the light-dependent arrhythmia observed in elj3 mutants is pleiotropic on multiple outputs regardless of phase. Plants overexpressing ELF3 have an increased period length in constant light and flower late in long-days; furthermore, etiolated ELF3-overexpressing seedlings exhibit a decreased acute CAB2 response after a red light pulse, whereas the null mutant is hypersensitive to acute induction. This finding suggests that ELF3 negatively regulates light input to both the clock and its outputs. To determine whether ELF3's action is phase dependent, we examined clock resetting by light pulses and constructed phase response curves. Absence of ELF3 activity causes a significant alteration of the phase response curve during the subjective night, and overexpression of ELF3 results in decreased sensitivity to the resetting stimulus, suggesting that ELF3 antagonizes light input to the clock during the night. Indeed, the ELF3 protein interacts with the photoreceptor PHYB in the yeast two-hybrid assay and in vitro. The phase ofELF3 function correlates with its peak expression levels of transcript and protein in the subjective night. ELF3 action, therefore, represents a mechanism by which the oscillator modulates light resetting. Furthermore, flowering time is dependent upon proper expression ofELF3. Scientifically, we've made a big leap in the understanding of the circadian system and how it is coupled so tightly with light reception in terms of period length and clock resetting. Agriculturally, understanding more about the way in which the clock perceives and relays temporal information to pathways such as those involved in the floral transition can lead to increased crop yields by enabling plants to be grown in suboptimal conditions.