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Articoli di riviste sul tema "Balance locale Excitation"
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Umar, A., S. Ahmad e T. K. Datta. "Stability Analysis of a Moored Vessel". Journal of Offshore Mechanics and Arctic Engineering 126, n. 2 (1 maggio 2004): 164–74. http://dx.doi.org/10.1115/1.1710873.
Testo completoAbstract (sommario):
A procedure for the stability analysis of a slack mooring system is presented for periodic wave excitation by finding its approximate response using a two term harmonic balance method (HBM). The conditions for determining the local and global stability of the approximate solutions are established using Hill’s variational approach and Floquet’s theory. A number of instability phenomena are identified for the mooring system for certain frequencies of excitations which fall outside the range of frequencies obtained from the analytically derived stability boundaries. The instability phenomena include symmetry breaking bifurcation, subharmonics, 3T and 5T solutions. Even chaotic motion is exhibited under certain cases.
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Hamaguchi, Kosuke, Alexa Riehle e Nicolas Brunel. "Estimating Network Parameters From Combined Dynamics of Firing Rate and Irregularity of Single Neurons". Journal of Neurophysiology 105, n. 1 (gennaio 2011): 487–500. http://dx.doi.org/10.1152/jn.00858.2009.
Testo completoAbstract (sommario):
High firing irregularity is a hallmark of cortical neurons in vivo, and modeling studies suggest a balance of excitation and inhibition is necessary to explain this high irregularity. Such a balance must be generated, at least partly, from local interconnected networks of excitatory and inhibitory neurons, but the details of the local network structure are largely unknown. The dynamics of the neural activity depends on the local network structure; this in turn suggests the possibility of estimating network structure from the dynamics of the firing statistics. Here we report a new method to estimate properties of the local cortical network from the instantaneous firing rate and irregularity (CV2) under the assumption that recorded neurons are a part of a randomly connected sparse network. The firing irregularity, measured in monkey motor cortex, exhibits two features; many neurons show relatively stable firing irregularity in time and across different task conditions; the time-averaged CV2 is widely distributed from quasi-regular to irregular (CV2 = 0.3–1.0). For each recorded neuron, we estimate the three parameters of a local network [balance of local excitation-inhibition, number of recurrent connections per neuron, and excitatory postsynaptic potential (EPSP) size] that best describe the dynamics of the measured firing rates and irregularities. Our analysis shows that optimal parameter sets form a two-dimensional manifold in the three-dimensional parameter space that is confined for most of the neurons to the inhibition-dominated region. High irregularity neurons tend to be more strongly connected to the local network, either in terms of larger EPSP and inhibitory PSP size or larger number of recurrent connections, compared with the low irregularity neurons, for a given excitatory/inhibitory balance. Incorporating either synaptic short-term depression or conductance-based synapses leads many low CV2 neurons to move to the excitation-dominated region as well as to an increase of EPSP size.
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Mariño, Jorge, James Schummers, David C. Lyon, Lars Schwabe, Oliver Beck, Peter Wiesing, Klaus Obermayer e Mriganka Sur. "Invariant computations in local cortical networks with balanced excitation and inhibition". Nature Neuroscience 8, n. 2 (23 gennaio 2005): 194–201. http://dx.doi.org/10.1038/nn1391.
Testo completo
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Zheng, Ying, Jing Jing Luo, Sam Harris, Aneurin Kennerley, Jason Berwick, Steve A. Billings e John Mayhew. "Balanced excitation and inhibition: Model based analysis of local field potentials". NeuroImage 63, n. 1 (ottobre 2012): 81–94. http://dx.doi.org/10.1016/j.neuroimage.2012.06.040.
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Lattuada, Enrico, Stefano Buzzaccaro e Roberto Piazza. "Thermophoresis in self-associating systems: probing poloxamer micellization by opto-thermal excitation". Soft Matter 15, n. 10 (2019): 2140–51. http://dx.doi.org/10.1039/c8sm02386g.
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Renart, Alfonso, Rubén Moreno-Bote, Xiao-Jing Wang e Néstor Parga. "Mean-Driven and Fluctuation-Driven Persistent Activity in Recurrent Networks". Neural Computation 19, n. 1 (gennaio 2007): 1–46. http://dx.doi.org/10.1162/neco.2007.19.1.1.
Testo completoAbstract (sommario):
Spike trains from cortical neurons show a high degree of irregularity, with coefficients of variation (CV) of their interspike interval (ISI) distribution close to or higher than one. It has been suggested that this irregularity might be a reflection of a particular dynamical state of the local cortical circuit in which excitation and inhibition balance each other. In this “balanced” state, the mean current to the neurons is below threshold, and firing is driven by current fluctuations, resulting in irregular Poisson-like spike trains. Recent data show that the degree of irregularity in neuronal spike trains recorded during the delay period of working memory experiments is the same for both low-activity states of a few Hz and for elevated, persistent activity states of a few tens of Hz. Since the difference between these persistent activity states cannot be due to external factors coming from sensory inputs, this suggests that the underlying network dynamics might support coexisting balanced states at different firing rates. We use mean field techniques to study the possible existence of multiple balanced steady states in recurrent networks of current-based leaky integrate-and-fire (LIF) neurons. To assess the degree of balance of a steady state, we extend existing mean-field theories so that not only the firing rate, but also the coefficient of variation of the interspike interval distribution of the neurons, are determined self-consistently. Depending on the connectivity parameters of the network, we find bistable solutions of different types. If the local recurrent connectivity is mainly excitatory, the two stable steady states differ mainly in the mean current to the neurons. In this case, the mean drive in the elevated persistent activity state is suprathreshold and typically characterized by low spiking irregularity. If the local recurrent excitatory and inhibitory drives are both large and nearly balanced, or even dominated by inhibition, two stable states coexist, both with subthreshold current drive. In this case, the spiking variability in both the resting state and the mnemonic persistent state is large, but the balance condition implies parameter fine-tuning. Since the degree of required fine-tuning increases with network size and, on the other hand, the size of the fluctuations in the afferent current to the cells increases for small networks, overall we find that fluctuation-driven persistent activity in the very simplified type of models we analyze is not a robust phenomenon. Possible implications of considering more realistic models are discussed.
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Wang, Jiang, Ruixue Han, Xilei Wei, Yingmei Qin, Haitao Yu e Bin Deng. "Weak signal detection and propagation in diluted feed-forward neural network with recurrent excitation and inhibition". International Journal of Modern Physics B 30, n. 02 (20 gennaio 2016): 1550253. http://dx.doi.org/10.1142/s0217979215502537.
Testo completoAbstract (sommario):
Reliable signal propagation across distributed brain areas provides the basis for neural circuit function. Modeling studies on cortical circuits have shown that multilayered feed-forward networks (FFNs), if strongly and/or densely connected, can enable robust signal propagation. However, cortical networks are typically neither densely connected nor have strong synapses. This paper investigates under which conditions spiking activity can be propagated reliably across diluted FFNs. Extending previous works, we model each layer as a recurrent sub-network constituting both excitatory (E) and inhibitory (I) neurons and consider the effect of interactions between local excitation and inhibition on signal propagation. It is shown that elevation of cellular excitation–inhibition (EI) balance in the local sub-networks (layers) softens the requirement for dense/strong anatomical connections and thereby promotes weak signal propagation in weakly connected networks. By means of iterated maps, we show how elevated local excitability state compensates for the decreased gain of synchrony transfer function that is due to sparse long-range connectivity. Finally, we report that modulations of EI balance and background activity provide a mechanism for selectively gating and routing neural signal. Our results highlight the essential role of intrinsic network states in neural computation.
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Anticevic, Alan, e John Lisman. "How Can Global Alteration of Excitation/Inhibition Balance Lead to the Local Dysfunctions That Underlie Schizophrenia?" Biological Psychiatry 81, n. 10 (maggio 2017): 818–20. http://dx.doi.org/10.1016/j.biopsych.2016.12.006.
Testo completo
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Brunel, Nicolas, e Xiao-Jing Wang. "What Determines the Frequency of Fast Network Oscillations With Irregular Neural Discharges? I. Synaptic Dynamics and Excitation-Inhibition Balance". Journal of Neurophysiology 90, n. 1 (luglio 2003): 415–30. http://dx.doi.org/10.1152/jn.01095.2002.
Testo completoAbstract (sommario):
When the local field potential of a cortical network displays coherent fast oscillations (∼40-Hz gamma or ∼200-Hz sharp-wave ripples), the spike trains of constituent neurons are typically irregular and sparse. The dichotomy between rhythmic local field and stochastic spike trains presents a challenge to the theory of brain rhythms in the framework of coupled oscillators. Previous studies have shown that when noise is large and recurrent inhibition is strong, a coherent network rhythm can be generated while single neurons fire intermittently at low rates compared to the frequency of the oscillation. However, these studies used too simplified synaptic kinetics to allow quantitative predictions of the population rhythmic frequency. Here we show how to derive quantitatively the coherent oscillation frequency for a randomly connected network of leaky integrate-and-fire neurons with realistic synaptic parameters. In a noise-dominated interneuronal network, the oscillation frequency depends much more on the shortest synaptic time constants (delay and rise time) than on the longer synaptic decay time, and ∼200-Hz frequency can be realized with synaptic time constants taken from slice data. In a network composed of both interneurons and excitatory cells, the rhythmogenesis is a compromise between two scenarios: the fast purely interneuronal mechanism, and the slower feedback mechanism (relying on the excitatory-inhibitory loop). The properties of the rhythm are determined essentially by the ratio of time scales of excitatory and inhibitory currents and by the balance between the mean recurrent excitation and inhibition. Faster excitation than inhibition, or a higher excitation/inhibition ratio, favors the feedback loop and a much slower oscillation (typically in the gamma range).
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Jenkins, Edward B. "A Thermal Pressure Inside the Local Bubble, as Revealed by CI Fine-Structure Excitation". International Astronomical Union Colloquium 166 (1997): 33–36. http://dx.doi.org/10.1017/s0252921100070676.
Testo completoAbstract (sommario):
AbstractUltraviolet absorption lines from carbon atoms within a neutral cloud inside or near the edge of the Local Bubble can reveal the thermal pressure of the gas, since the relative populations of the fine-structure levels are determined by a balance between collisional excitation and radiative decay. Features from a C I multiplet appearing in the uv spectrum of the star δ Cyg (l = 79°, b = +10°, d = 52 pc) were observed with the echelle spectrograph of the Goddard High Resolution Spectrograph on HST. An interpretation of absorptions detected from the two lowest levels gives a thermal pressure range 102.7 < p/k < 103.7 cm−3K.
Tesi sul tema "Balance locale Excitation"
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Vallet, Anais. "Etude de la balance Excitatiοn/Ιnhibitiοn de régiοns cérébrales impliquées dans une tâche de cοntrôle inhibiteur : mοdélisatiοn de dοnnées οbtenues en Ιmagerie par Résοnance Μagnétique fοnctiοnnelle et inversiοn". Electronic Thesis or Diss., Normandie, 2024. http://www.theses.fr/2024NORMC014.
Testo completoAbstract (sommario):
En psychologie, le contrôle inhibiteur est un mécanisme cognitif qui permet de stopper une ré-ponse motrice, émotionnelle ou cognitive non adaptée pour la réalisation d’un but désiré. Au niveaucérébral, le contrôle inhibiteur est associé au fonctionnement en réseau de régions cérébrales, quipeut être mesuré à partir du signal BOLD en IRMf. Des régions de contrôle préfrontales abaissentl’activité BOLD de régions cibles. L’IRMf permet de mesurer de manière indirecte l’activité desneurones. Comment peut-on alors inférer à partir de données d’IRMf des propriétés excitatriceset inhibitrices (E/I) neurales au sein de régions cérébrales impliquées dans une tâche de contrôleinhibiteur ?Nous partons d’un modèle biophysique non linéaire, hiérarchique qui décrit les évolutions tempo-relles des activités neurales excitatrice et inhibitrice par région (Naskar et al., 2021). Ces varia-tions d’activité produisent des changements BOLD dans chaque région cérébrale. L’analyse de cemodèle nous permet de : 1) identifier des paramètres neuraux de la balance E/I ; 2) montrer quel’augmentation d’activité BOLD d’une région de contrôle ne permet pas d’abaisser l’activité BOLDd’une région cible parce que les régions sont connectées par leurs neurones excitateurs uniquement ;3) proposer une nouvelle architecture de connectivité pour le permettre ; 4) étudier comment labaisse d’activité de la région cible dépend de la balance E/I dans la cible. Nous proposons alorsune nouvelle procédure d’inversion. Nous en vérifions la fiabilité avec des simulations, avant deprésenter une preuve de concept sur les données d’un sujet pendant une tâche de Think/NoThink,un paradigme d’étude du contrôle inhibiteur des intrusions mnésiques (Mary et al., 2020)In psychology, inhibitory control is a cognitive mechanism that stops a motor, emotional orcognitive response from achieving a desired goal. At cerebral level, inhibitory control is associatedwith a network of brain regions, whose function may be measured using BOLD signals from fMRI.Prefrontal control regions lower the BOLD activity of target regions. fMRI provides an indirectmeasure of the activity of neurons. How can we then infer from fMRI data, neural excitatory andinhibitory (E/I) properties of brain regions involved in an inhibitory control task ?We start with a non-linear biophysical model that describes by region the temporal evolutionof neural excitatory and inhibitory activities (Naskar et al., 2021). These variations in activityproduce BOLD changes in each brain region. Analysis of this model enables us to : 1) identifyneural parameters of the E/I balance ; 2) show that increasing the BOLD activity of a controlregion does not lower the BOLD activity of a target region, since these regions are connected bytheir excitatory neurons only ; 3) propose a new connectivity architecture to enable this ; 4) studyhow the lowering of activity in the target region depends on the E/I balance in the target region.We then propose a new inversion procedure. We check its reliability through simulations, beforepresenting a proof-of-concept using real data from a subject during a Think/No-Think task, aparadigm used for studying the inhibitory control of memory intrusions (Mary et al., 2020)
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Luo, Jingjing. "Modelling evoked local field potentials : an investigation into balanced synaptic excitation and inhibition". Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/6143/.
Testo completoCapitoli di libri sul tema "Balance locale Excitation"
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McCormick, David A., You-Sheng Shu e Andrea Hasenstaub. "Balanced Recurrent Excitation and Inhibition in Local Cortical Networks". In Excitatory-Inhibitory Balance, 113–24. Boston, MA: Springer US, 2003. http://dx.doi.org/10.1007/978-1-4615-0039-1_8.
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Benarroch, Eduardo E. "Peripheral and Spinal Mechanisms of Nociception". In Neuroscience for Clinicians, a cura di Eduardo E. Benarroch, 655–73. Oxford University Press, 2021. http://dx.doi.org/10.1093/med/9780190948894.003.0035.
Testo completoAbstract (sommario):
Pain is a conscious subjective experience driven by activity of nociceptors. Pain includes not only nociception but also abnormal transmission and processing of painful stimuli. Nociception involves unmyelinated and small myelinated fibers from small dorsal root ganglion neurons that respond to noxious heat, mechanical, or chemically stimuli. These neurons are functional and biochemically heterogeneous in terms of their sensitivity to stimuli, type of afferent axons, neurochemical composition, and targets in the dorsal horn. They activate both second-order projection neurons and different subsets of excitatory and inhibitory interneurons that have a major role in processing of sensory information. Mutations affecting ion channels in nociceptors, inflammatory mediators, or peripheral nerve injury trigger changes and expression of ion channels and receptors. This results in increased excitability of nociceptors, known as peripheral sensitization. Abnormal activity in nociceptors triggers plastic channels in the dorsal horn resulting in altered balance between excitation and inhibition, resulting in central sensitization. Local activation of microglia and astrocytes plays a major role in this process. Elucidation of mechanisms of peripheral and central sensitization provide insight into the pathophysiology of neuropathic pain and potential therapeutic targets for its treatment.
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Murphy, Allison J., e Farran Briggs. "Structure and Function of Corticothalamic Pathways of Layer 6 Neurons". In The Cerebral Cortex and Thalamus, a cura di Francisco Clasca e Sonja B. Hofer, 143–51. Oxford University PressNew York, 2023. http://dx.doi.org/10.1093/med/9780197676158.003.0014.
Testo completoAbstract (sommario):
Abstract Throughout the brain, corticothalamic (CT) neurons project from layer 6 of the cerebral cortex to various regions of the thalamus, including first-order thalamic nuclei that receive input from the sensory periphery and higher-order thalamic nuclei that derive their inputs mainly from cortical areas. Layer 6 CT neurons are diverse in terms of their cellular morphology and physiological properties, and they likely subserve a number of heterogeneous functions. While the number of synapses originating from layer 6 CT neurons onto thalamic cells is large, their terminals are distally located, small in size, and produce small, facilitating excitatory postsynaptic potentials, all characteristics that define these synaptic interactions as “modulatory” rather than “driving.” Importantly, layer 6 CT circuits often include axon collaterals that target inhibitory neuronal populations within the thalamus, enabling CT feedback to dynamically regulate the balance of excitation and inhibition among thalamic neurons. Although much is yet to be learned about the function of layer 6 CT feedback in the thalamus, current evidence from sensory systems suggests that CT feedback can shape the tuning properties of thalamic neurons as well as influence the timing and precision with which thalamic cells encode incoming sensory information. Other functions of layer 6 CT feedback include regulating arousal state, attention, and sleep. Overall, layer 6 CT pathways provide diverse inputs to thalamus that are likely critical for multiple aspects of brain function.
Atti di convegni sul tema "Balance locale Excitation"
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Zellhuber, M., C. Meraner, R. Kulkarni, W. Polifke e B. Schuermans. "Large Eddy Simulation of Flame Response to Transverse Acoustic Excitation in a Model Reheat Combustor". In ASME Turbo Expo 2012: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/gt2012-68317.
Testo completoAbstract (sommario):
The response of a perfectly premixed, turbulent jet flame at elevated inflow temperature to high frequency flow perturbations is investigated. A generic reheat burner geometry is considered, where the spatial distribution of heat release is controlled by auto-ignition in the jet core on the one hand, and kinematic balance between flow and flame propagation in the shear layers between the jet and the external recirculation zones on the other. To model auto-ignition and heat release in compressible turbulent flow, a progress variable / stochastic fields formulation adapted for the LES context is used. Flow field perturbations corresponding to transverse acoustic modes are imposed by harmonic excitation of velocity at the combustor boundaries. Simulations with single-frequency excitation are carried out in order to study the flame response to transverse fluctuations of velocity. Heat release fluctuations are observed predominantly in the shear layers, where flame propagation is important. The flow-flame coupling in these regions is analysed in detail with a filter-based post-processing approach, invoking a local Rayleigh index and providing insight into the interactions of flame wrinkling by vorticity and convection due to mean and fluctuating velocity.
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Malla, Arun, Joshua LeGrande, Mohammad Bukhari e Oumar Barry. "Introduction of Local Resonators to a Nonlinear Metamaterial With Topological Features". In ASME 2023 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/detc2023-116669.
Testo completoAbstract (sommario):
Abstract Metamaterials have been shown to benefit from the addition of local resonators, nonlinear elements, or topological properties, gaining features such as additional bandgaps and localized vibration modes. However, there is currently no work in the literature that examines a metamaterial system including all three elements. In this work, we model a 1-dimensional metamaterial lattice as a spring-mass chain with coupled local resonators. Quasiperiodic modulation in the nonlinear connecting springs is utilized to achieve topological features. For comparison, a similar system without local resonators is also modeled. Both analytical and numerical methods are used to study this system. The infinite chain response of the proposed system is solved through the perturbation method of multiple scales. This analytical solution is compared to the finite chain response, estimated using the method of harmonic balance and solved numerically. The resulting band structures and mode shapes are used to study the effects of quasiperiodic parameters and excitation amplitude on the system behavior both with and without the presence of local resonators. Specifically, the impact of local resonators on topological features such as edge modes is established, demonstrating the appearance of a trivial bandgap and multiple localized edge states for both main cells and local resonators.
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Laxalde, Denis, Jean-Jacques Sinou, Fabrice Thouverez e Jean-Pierre Lombard. "Modeling and Analysis of Friction Rim Dampers for Blisks". In ASME 2005 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/detc2005-84417.
Testo completoAbstract (sommario):
A damping strategy for blisks of turbomachinery involving a friction rim is investigated. These rims, located in grooves underside the wheel of the blisks, are held in by centrifugal loads and the energy is dissipated when relative motions between the rim and the disk occur. A method of dynamical analysis of a cyclic blisk nonlinearly coupled with a split rim is presented: the steady-state response being calculated using an multi-harmonic balance method. Numerical simulations on a lumped-parameter model are presented for several damper characteristics and several excitation configurations. From these results, the performance of this damping strategy is discussed and some design guidelines are given. Finally the influence of mistuning on the damping performances is analysed.
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Orynyak, Igor, Iaroslav Dubyk e Anatolii Batura. "Energy Approach for Determine Frequency and Amplitude of Vibration of Piping With Closed Side Branches". In ASME 2015 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/pvp2015-45289.
Testo completoAbstract (sommario):
This article suggests calculation method for frequency and amplitude of acoustic vibration in piping with closed side branches, caused by gaseous running flow. The calculation algorithm consists of following steps: i) local excitation system is defined; ii) different combinations of boundary conditions are formed; iii) for fixed pair of boundary conditions ratio of stored in system energy and radiated from boundaries energy is written; iv) for every frequency energy functional is maximized to find boundary conditions; v) resonance frequencies are determined from plotting a curve of maximal energy ratio vs. frequency. Energy approach was further developed to analyze amplitude of vibration. For amplitude determine balance between injected energy (which depends on the Strouhal number and is defined from experimental data for laboratory geometries), and radiated from boundaries energy is written.
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Biesinger, Thomas, Maximilian Kölzer, Alexander Schukmann, Harald Roclawski, Marc Kainz, Philippe Godin, Juan Carlos Morales e Laith Zori. "Application of the Harmonic Balance Method for Large Spread Multiple Frequency Scales". In ASME Turbo Expo 2022: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/gt2022-79393.
Testo completoAbstract (sommario):
Abstract This paper presents the application of the harmonic balance method to periodic turbomachinery flow problems containing multiple fundamental frequencies. It is well known that the solution convergence of a transient turbomachinery flow using classical integration methods is computationally intensive and requires the integration for multiple periods to achieve a converged periodic solution. The computational effort is even higher when multiple fundamental frequencies (vastly different time scales) are modeled since the time stepping required is limited by the higher frequency in the flow. Unlike the classical time integration methods, the multifrequency harmonic balance method is very well suited for these applications since it allows for much faster calculations than the standard time marching algorithms. In addition, to resolve all the fundamental frequencies and higher harmonics, the current implementation of the harmonic balance method allows for solutions on unequal time interval distributions of the time planes. Given a user-defined list of frequencies that govern the flow problem, this method utilizes an optimization strategy to compute the time planes. There are two simulation cases of interest: aerodynamic performance and forced response analyses, both with different accuracy requirements. The number of required frequencies is dependent on the goal of the simulation. For aerodynamic performance analysis, global quantities such efficiency, pressure ratio, etc. can be predicted with fewer fundamental frequencies than forced response analysis where accurate local flow details demand a higher number of fundamental frequencies. The advantages of the multifrequency harmonic balance are illustrated by modeling two radial turbine configurations subjected to an inlet pulse from a reciprocating engine. Not only the expected trends such as higher-modes modeling granularity and time transient accuracy are shown, but also the calculations agree well with experimental data. The computational effort can be up to tenfold lower than the standard time-marching simulations. Machine aerodynamic performance predictions from the harmonic balance method are compared to accurate time-marching solutions and experimental data measurements. The efficiency of the computation is also discussed. The second example will compare the predicted surface excitation from the harmonic balance method vs. the time-marching solution.
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Prior, Jack, Luke Bates, Steve Whelan, Byron Mason, James Knowles e Richard Stocker. "Automatic Parameter Scheduling of Equivalent Circuit Battery Models Using Local Linear Model Trees and Amplitude-Modulated Pseudo-Random Excitation Signals". In Energy & Propulsion Conference & Exhibition. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International, 2024. http://dx.doi.org/10.4271/2024-01-4328.
Testo completoAbstract (sommario):
<div class="section abstract"><div class="htmlview paragraph">The automotive industry is moving rapidly to electrification through development of Battery Electric Vehicles (BEV). Development and sizing of the battery and powertrain requires a detailed understanding of battery cell behavior under different conditions. Achieving this is difficult due to the range of cells available and the large range of condition variables of each cell. Equivalent-circuit models are used for BEV development. However, conventional battery cell characterization testing to parameterize these models are time and resource intensive. Characterization can be performed using well-known techniques such as Hybrid Pulse Power Characterization (HPPC) or Galvanostatic Intermittent Titration Technique (GITT) which are used to optimize parameters of an ESC model pertinent to the dynamics of its voltage response. However, the discrete State-of-Charge (SoC) intervals and demand current amplitudes of these experiments are not optimized for a balance of time and model effectiveness. There is scope to develop methods that can excite a range of current amplitudes and SoC points in a shorter timeframe whilst revealing non-linearities in the system’s time response. In this work an excitation signal design is presented that aims to maximize the amount of information gained about the dynamics of the battery across the SOC range within a short timeframe. An automated means of parameter-scheduling an ESC model is also introduced to best utilise the data from such a randomized, unstructured experiment. The excitation signal design takes the form of pulse signals with pseudo-randomly generated amplitudes and duration, constrained to ensure a specified test duration. This data is used to characterize a variant of the ESC model that automatically schedules parameters of the model via self-organizing Locally Linear Model Trees (LoLiMoT). The resulting models have strong predictive capability even in the extreme low SOC condition, resulting in an 18% reduction in Mean Absolute Error when compared to an ESC model without parameter scheduling over a validation cycle. This constitutes a strong step toward rapid, robust battery modelling processes for the purpose of cell selection and simulation for powertrain/vehicle design.</div></div>
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Inada, Fumio, Takashi Nishihara e Jun Mizutani. "Fluid-Elastic Vibration of Cross-Shaped Tube Bundle in Mixed Cross and Parallel Flow: Measurement of Gap Flow Velocity and Vibration Characteristics". In ASME 2006 Pressure Vessels and Piping/ICPVT-11 Conference. ASMEDC, 2006. http://dx.doi.org/10.1115/pvp2006-icpvt-11-93900.
Testo completoAbstract (sommario):
A cross-shaped control rod guide tube bundle is proposed for the lower plenum structure in the next-generation LWR, ABWR-II. In our previous studies, we measured the local fluid excitation forces acting on a cross-shaped tube bundle as well as the self-excited vibration characteristics in pure cross flow in water tunnel tests. In the reactor conditions, the flow field around the tube bundles contains mixed cross and parallel flow components. In this study, water tunnel tests under mixed cross and parallel flow conditions were preformed to understand the influence of the balance of parallel and cross flow components on vibration response. The distributions of the flow direction and flow velocity in the gap between the adjacent tubes were measured with circular Pilot tubes in detail. It was found that the critical flow velocity of self-excited vibration was not influenced by the parallel flow component, but depended only on the cross flow component.
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Huang, Jianliang, e Weidong Zhu. "A New Incremental Harmonic Balance Method With Two Time Scales for Quasi-Periodic Motions of an Axially Moving Beam With Internal Resonance Under Single-Tone External Excitation". In ASME 2019 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/imece2019-12153.
Testo completoAbstract (sommario):
Abstract In this work, a new incremental harmonic balance (IHB) method with two time scales, where one is a fundamental frequency, and the other is an interval distance of two adjacent frequencies, is proposed for quasi-periodic motions of an axially moving beam with three-to-one internal resonance under singletone external excitation. It is found that the interval frequency of every two adjacent frequencies, located around the fundamental frequency or one of its integer multiples, is fixed due to nonlinear coupling among resonant vibration modes. Consequently, only two time scales are used in the IHB method to obtain all incommensurable frequencies of quasi-periodic motions of the axially moving beam. The present IHB method can accurately trace from periodic responses of the beam to its quasi-periodic motions. For periodic responses of the axially moving beam, the single fundamental frequency is used in the IHB method to obtain solutions. For quasi-periodic motions of the beam, the present IHB method with two time scales is used, along with an amplitude increment approach that includes a large number of harmonics, to determine all the frequency components. All the frequency components and their corresponding amplitudes, obtained from the present IHB method, are in excellent agreement with those from numerical integration using the fourth-order Runge-Kutta method.
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Zhang, Bo, Xi Chen, Fengguang Xiang, Xiaohua Gan e Guangming Ren. "Dynamic Characteristics of Rotor-SFD-Support System Excited by Base Harmonic Excitations Using MHB-AFT Method". In ASME Turbo Expo 2022: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/gt2022-82536.
Testo completoAbstract (sommario):
Abstract When operating at high speed, aeroengines mounted on the aircrafts also perform complicated maneuvering flights along with the aircrafts. The engine rotor systems will undergo forced motions excited by base movements and mass unbalance, which may lead to severe vibrations. Squeeze film damper (SFD) is generally used for vibration damping in aeroengine, but it also introduces structural nonlinearity like bistable jump. Moreover, the reliability of SFD is also affected by base excitations. Therefore, it is necessary to investigate the nonlinear dynamic behavior of rotor-SFD-support system excited by base motions. Taking a muti-disk rotor shaft supported by two SFDs with squirrel cages as the research object to simulate a gas generator in a turboshaft engine, the steady-state responses of the rotor system were calculated by multi-dimensional harmonic balance combined with alternating frequency/time domain method (MHB-AFT). The effects of base harmonic rotations and mass unbalance on steady-state responses of rotor system were investigated. The results indicate that the time-varying parametric excitations of base motions have strong effects on amplitude-frequency response of transverse displacement of rotor system. The critical speeds and resonant amplitudes of responses change with the magnitude and frequency of several base harmonic rotations. The variation of the frequency of base harmonic motion has the most significant impact on the amplitude-frequency response of transverse displacement of rotor system. The increase of base harmonic frequency will lead to multiple local peaks in the response curves, especially in the case of base harmonic rolling motion. In addition, the combination of base harmonic rotation around pitching and yawing axes results in significantly different response characteristics. Therefore, the influence of base harmonic motions should be considered during the structural design and damping optimization of SFDs.
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Gharavi, Ali, e Gary L. McPherson. "Visible to UV up-conversion luminescence from Er3+ doped crystals of CsMgCl3". In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1992. http://dx.doi.org/10.1364/oam.1992.mj5.
Testo completoAbstract (sommario):
Strong UV emission has been observed in crystals of CsMgCl3 doped with Er3+ ions when pumped with 546 to 550 nm wavelengths. CsMgCl3 crystals exhibit a chain structure where two Er3+ ions replace three Mg2+ ions in the chain, preserving the local charge balance forming discrete defined pairs. The UV emission is observable at temperatures between 10 and 297 K. At 10 K the intensity of the UV emission is comparable to the emissions from the pumped state. The experiments performed in our lab show that the up-conversion is a second order process due to energy transfer between simultaneously excited Er3+ pairs involving two 4S3/2 states, raising the energy of one Er3+ sight to twice the energy (4G9/2). Energy migration through the crystal and other doubly excited pairs also results in weak up-conversion emissions. The strongest UV emissions are due to transitions from 4G9/2 to 4I13/2(338 nm) and 4G11/2 to 4I13/2 (377 nm). Because of thermal population of the sublevels within the ground state (4I15/2) manifold, a number of red shifted features (hot bands) appear in the excitation spectrum as the temperature is raised from 10 to 297 K.
Rapporti di organizzazioni sul tema "Balance locale Excitation"
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Wu, Yingjie, Selim Gunay e Khalid Mosalam. Hybrid Simulations for the Seismic Evaluation of Resilient Highway Bridge Systems. Pacific Earthquake Engineering Research Center, University of California, Berkeley, CA, novembre 2020. http://dx.doi.org/10.55461/ytgv8834.
Testo completoAbstract (sommario):
Bridges often serve as key links in local and national transportation networks. Bridge closures can result in severe costs, not only in the form of repair or replacement, but also in the form of economic losses related to medium- and long-term interruption of businesses and disruption to surrounding communities. In addition, continuous functionality of bridges is very important after any seismic event for emergency response and recovery purposes. Considering the importance of these structures, the associated structural design philosophy is shifting from collapse prevention to maintaining functionality in the aftermath of moderate to strong earthquakes, referred to as “resiliency” in earthquake engineering research. Moreover, the associated construction philosophy is being modernized with the utilization of accelerated bridge construction (ABC) techniques, which strive to reduce the impact of construction on traffic, society, economy and on-site safety. This report presents two bridge systems that target the aforementioned issues. A study that combined numerical and experimental research was undertaken to characterize the seismic performance of these bridge systems. The first part of the study focuses on the structural system-level response of highway bridges that incorporate a class of innovative connecting devices called the “V-connector,”, which can be used to connect two components in a structural system, e.g., the column and the bridge deck, or the column and its foundation. This device, designed by ACII, Inc., results in an isolation surface at the connection plane via a connector rod placed in a V-shaped tube that is embedded into the concrete. Energy dissipation is provided by friction between a special washer located around the V-shaped tube and a top plate. Because of the period elongation due to the isolation layer and the limited amount of force transferred by the relatively flexible connector rod, bridge columns are protected from experiencing damage, thus leading to improved seismic behavior. The V-connector system also facilitates the ABC by allowing on-site assembly of prefabricated structural parts including those of the V-connector. A single-column, two-span highway bridge located in Northern California was used for the proof-of-concept of the proposed V-connector protective system. The V-connector was designed to result in an elastic bridge response based on nonlinear dynamic analyses of the bridge model with the V-connector. Accordingly, a one-third scale V-connector was fabricated based on a set of selected design parameters. A quasi-static cyclic test was first conducted to characterize the force-displacement relationship of the V-connector, followed by a hybrid simulation (HS) test in the longitudinal direction of the bridge to verify the intended linear elastic response of the bridge system. In the HS test, all bridge components were analytically modeled except for the V-connector, which was simulated as the experimental substructure in a specially designed and constructed test setup. Linear elastic bridge response was confirmed according to the HS results. The response of the bridge with the V-connector was compared against that of the as-built bridge without the V-connector, which experienced significant column damage. These results justified the effectiveness of this innovative device. The second part of the study presents the HS test conducted on a one-third scale two-column bridge bent with self-centering columns (broadly defined as “resilient columns” in this study) to reduce (or ultimately eliminate) any residual drifts. The comparison of the HS test with a previously conducted shaking table test on an identical bridge bent is one of the highlights of this study. The concept of resiliency was incorporated in the design of the bridge bent columns characterized by a well-balanced combination of self-centering, rocking, and energy-dissipating mechanisms. This combination is expected to lead to minimum damage and low levels of residual drifts. The ABC is achieved by utilizing precast columns and end members (cap beam and foundation) through an innovative socket connection. In order to conduct the HS test, a new hybrid simulation system (HSS) was developed, utilizing commonly available software and hardware components in most structural laboratories including: a computational platform using Matlab/Simulink [MathWorks 2015], an interface hardware/software platform dSPACE [2017], and MTS controllers and data acquisition (DAQ) system for the utilized actuators and sensors. Proper operation of the HSS was verified using a trial run without the test specimen before the actual HS test. In the conducted HS test, the two-column bridge bent was simulated as the experimental substructure while modeling the horizontal and vertical inertia masses and corresponding mass proportional damping in the computer. The same ground motions from the shaking table test, consisting of one horizontal component and the vertical component, were applied as input excitations to the equations of motion in the HS. Good matching was obtained between the shaking table and the HS test results, demonstrating the appropriateness of the defined governing equations of motion and the employed damping model, in addition to the reliability of the developed HSS with minimum simulation errors. The small residual drifts and the minimum level of structural damage at large peak drift levels demonstrated the superior seismic response of the innovative design of the bridge bent with self-centering columns. The reliability of the developed HS approach motivated performing a follow-up HS study focusing on the transverse direction of the bridge, where the entire two-span bridge deck and its abutments represented the computational substructure, while the two-column bridge bent was the physical substructure. This investigation was effective in shedding light on the system-level performance of the entire bridge system that incorporated innovative bridge bent design beyond what can be achieved via shaking table tests, which are usually limited by large-scale bridge system testing capacities.