Academic literature on the topic '4-8 Hz oscillation'
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Journal articles on the topic "4-8 Hz oscillation"
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Chen, Yvonne Y., and Jeremy B. Caplan. "Rhythmic Activity and Individual Variability in Recognition Memory: Theta Oscillations Correlate with Performance whereas Alpha Oscillations Correlate with ERPs." Journal of Cognitive Neuroscience 29, no. 1 (January 2017): 183–202. http://dx.doi.org/10.1162/jocn_a_01033.
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During study trials of a recognition memory task, alpha (∼10 Hz) oscillations decrease, and concurrently, theta (4–8 Hz) oscillations increase when later memory is successful versus unsuccessful (subsequent memory effect). Likewise, at test, reduced alpha and increased theta activity are associated with successful memory (retrieval success effect). Here we take an individual-differences approach to test three hypotheses about theta and alpha oscillations in verbal, old/new recognition, measuring the difference in oscillations between hit trials and miss trials. First, we test the hypothesis that theta and alpha oscillations have a moderately mutually exclusive relationship; but no support for this hypothesis was found. Second, we test the hypothesis that theta oscillations explain not only memory effects within participants, but also individual differences. Supporting this prediction, durations of theta (but not alpha) oscillations at study and at test correlated significantly with d′ across participants. Third, we test the hypothesis that theta and alpha oscillations reflect familiarity and recollection processes by comparing oscillation measures to ERPs that are implicated in familiarity and recollection. The alpha-oscillation effects correlated with some ERP measures, but inversely, suggesting that the actions of alpha oscillations on memory processes are distinct from the roles of familiarity- and recollection-linked ERP signals. The theta-oscillation measures, despite differentiating hits from misses, did not correlate with any ERP measure; thus, theta oscillations may reflect elaborative processes not tapped by recollection-related ERPs. Our findings are consistent with alpha oscillations reflecting visual inattention, which can modulate memory, and with theta oscillations supporting recognition memory in ways that complement the most commonly studied ERPs.
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Young, M. P., K. Tanaka, and S. Yamane. "On oscillating neuronal responses in the visual cortex of the monkey." Journal of Neurophysiology 67, no. 6 (June 1, 1992): 1464–74. http://dx.doi.org/10.1152/jn.1992.67.6.1464.
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1. Recent studies of visual processing in the cat have shown stimulus-related oscillations in the 30- to 70-Hz range. We sought to replicate these findings in the monkey. 2. We recorded multiunit activity (MUA) and local field potentials (LFP) in areas V1 and middle-temporal area (MT), and MUA from the inferotemporal cortex (IT) of monkeys (Macaca fuscata). Recordings in all areas were made under conditions of anesthesia as close as possible to those in previous studies of oscillating responses in the cat. In addition, we recorded MUA in the IT of behaving monkeys while the monkeys performed a face discrimination task. 3. In areas V1 and MT, LFP power spectra showed broadband increases (1-100 Hz) in amplitude on stimulation by swept optimally oriented light bars, and not a shift in power from low to midfrequency, as has been reported in the cat. 4. MUA autocorrelograms (ACGs) classified by fitting Gabor functions, showed oscillations at approximately 10% of recording sites in V1 and MT, but these oscillations were in the alpha range (12-13 Hz). 5. MUA ACGs from IT in the anesthetized monkey showed no oscillations. 6. For MUA ACGs from IT in the behaving monkey, only two recording sites (out of 50) showed an oscillating response, with frequencies of 44 and 48 Hz. One oscillating response was associated with stimulation, and the other was associated with the absence of stimulation. 7. The very low incidence in the monkey of oscillating responses in the 30- to 70-Hz range (2 in 424 recordings made at 142 recording sites) and the absence of stimulus dependence suggest that such oscillations are unlikely to serve a function in the monkey, and that there may be a species difference between monkey and cat in the dynamics of neural activity in the visual cortex. 8. We found that methods of classifying responses as oscillating used in some of the studies of the cat may have led to overestimation of both the number of sites showing oscillation and the number of pairs of sites showing phase coherence. These problems arise from the failure to take account of badness of fit between Gabor functions and their corresponding ACGs, and from Gabor functions "ringing" in response to short phasic phenomena that could be consistent with nonoscillatory activity.
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Yan, Qin, and Qingfang Zhang. "Theta Band (4–8 Hz) Oscillations Reflect Online Processing of Rhythm in Speech Production." Brain Sciences 12, no. 12 (November 22, 2022): 1593. http://dx.doi.org/10.3390/brainsci12121593.
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How speech prosody is processed in the brain during language production remains an unsolved issue. The present work used the phrase-recall paradigm to analyze brain oscillation underpinning rhythmic processing in speech production. Participants were told to recall target speeches aloud consisting of verb–noun pairings with a common (e.g., [2+2], the numbers in brackets represent the number of syllables) or uncommon (e.g., [1+3]) rhythmic pattern. Target speeches were preceded by rhythmic musical patterns, either congruent or incongruent, created by using pure tones at various temporal intervals. Electroencephalogram signals were recorded throughout the experiment. Behavioral results in 2+2 target speeches showed a rhythmic priming effect when comparing congruent and incongruent conditions. Cerebral-acoustic coherence analysis showed that neural activities synchronized with the rhythmic patterns of primes. Furthermore, target phrases that had congruent rhythmic patterns with a prime rhythm were associated with increased theta-band (4–8 Hz) activity in the time window of 400–800 ms in both the 2+2 and 1+3 target conditions. These findings suggest that rhythmic patterns can be processed online. Neural activities synchronize with the rhythmic input and speakers create an abstract rhythmic pattern before and during articulation in speech production.
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Goldreich, D., R. J. Krauzlis, and S. G. Lisberger. "Effect of changing feedback delay on spontaneous oscillations in smooth pursuit eye movements of monkeys." Journal of Neurophysiology 67, no. 3 (March 1, 1992): 625–38. http://dx.doi.org/10.1152/jn.1992.67.3.625.
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1. Our goal was to discriminate between two classes of models for pursuit eye movements. The monkey's pursuit system and both classes of model exhibit oscillations around target velocity during tracking of ramp target motion. However, the mechanisms that determine the frequency of oscillations differ in the two classes of model. In "internal feedback" models, oscillations are controlled by internal feedback loops, and the frequency of oscillation does not depend strongly on the delay in visual feedback. In "image motion" models, oscillations are controlled by visual feedback, and the frequency of oscillation does depend on the delay in visual feedback. 2. We measured the frequency of oscillation during pursuit of ramp target motion as a function of the total delay for visual feedback. For the shortest feedback delays of approximately 70 ms, the frequency of oscillation was between 6 and 7 Hz. Increases in feedback delay caused decreases in the frequency of oscillation. The effect of increasing feedback delay was similar, whether the increases were produced naturally by dimming and decreasing the size of the tracking target or artificially with the computer. We conclude that the oscillations in eye velocity during pursuit of ramp target motion are controlled by visual inputs, as suggested by the image motion class of models. 3. Previous experiments had suggested that the visuomotor pathways for pursuit are unable to respond well to frequencies as high as the 6-7 Hz at which eye velocity oscillates in monkeys. We therefore tested the response to target vibration at an amplitude of +/- 8 degrees/s and frequencies as high as 15 Hz. For target vibration at 6 Hz, the gain of pursuit, defined as the amplitude of eye velocity divided by the amplitude of target velocity, was as high as 0.65. We conclude that the visuomotor pathways for pursuit are capable of processing image motion at high temporal frequencies. 4. The gain of pursuit was much larger when the target vibrated around a constant speed of 15 degrees/s than when it vibrated around a stationary position. This suggests that the pursuit pathways contain a switch that must be closed to allow the visuomotor pathways for pursuit to operate at their full gain. The switch apparently remains open for target vibration around a stationary position. 5. The responses to target vibration revealed a frequency at which eye velocity lagged target velocity by 180 degrees and at which one monkey showed a local peak in the gain of pursuit.(ABSTRACT TRUNCATED AT 400 WORDS)
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Flint, A. C., and B. W. Connors. "Two types of network oscillations in neocortex mediated by distinct glutamate receptor subtypes and neuronal populations." Journal of Neurophysiology 75, no. 2 (February 1, 1996): 951–57. http://dx.doi.org/10.1152/jn.1996.75.2.951.
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1. Two distinct forms of spontaneous synchronous oscillations were investigated with field potential recordings in slices of rat somatosensory cortex in vitro. 2. The first type of synchronous oscillation was activated by low extracellular [Mg2+] and had dominant frequencies of 8-12 Hz. It was abolished reversibly by the N-methyl-D-aspartate (NMDA) receptor antagonists D-2-amino-5-phosphonovaleric acid and was relatively unaffected by the non-NMDA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX). The duration of oscillatory events was increased by blocking gamma-aminobuturic acid-A receptors with bicuculline or by activating metabotropic glutamate receptors with trans-1-aminocyclopentane-1,3-dicarboxylic acid. 3. A second form of synchronous oscillation was activated by acute application of kainic acid (10 microM), had dominant frequencies of 1-5 Hz, and was abolished reversibly by DNQX. Low concentrations of domoic acid mimicked the effects of kainate, but alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid or quisqualic acid did not, suggesting a role for the GluR5-7 and KA1-2 glutamate receptor subunits. 4. Surgical isolation of cortical layers showed that spontaneous NMDA receptor-dependent oscillations originated within layer 5 exclusively, but kainate receptor-dependent oscillations were uniquely generated by neurons in layers 2/3. 5. Our results suggest that neocortical neurons in layers 2/3 and layer 5 can independently generate two distinct forms of rhythmic population activity, each dependent upon activation of a different subtype of glutamate receptor.
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Leonard, Bridget L., Roger G. Evans, Michael A. Navakatikyan, and Simon C. Malpas. "Differential neural control of intrarenal blood flow." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 279, no. 3 (September 1, 2000): R907—R916. http://dx.doi.org/10.1152/ajpregu.2000.279.3.r907.
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To test whether renal sympathetic nerve activity (RSNA) can differentially regulate blood flow in the renal medulla (MBF) and cortex (CBF) of pentobarbital sodium-anesthetized rabbits, we electrically stimulated the renal nerves while recording total renal blood flow (RBF), CBF, and MBF. Three stimulation sequences were applied 1) varying amplitude (0.5–8 V), 2) varying frequency (0.5–8 Hz), and 3) a modulated sinusoidal pattern of varying frequency (0.04–0.72 Hz). Increasing amplitude or frequency of stimulation progressively decreased all flow variables. RBF and CBF responded similarly, but MBF responded less. For example, 0.5-V stimulation decreased CBF by 20 ± 9%, but MBF fell by only 4 ± 6%. The amplitude of oscillations in all flow variables was progressively reduced as the frequency of sinusoidal stimulation was increased. An increased amplitude of oscillation was observed at 0.12 and 0.32 Hz in MBF and to a lesser extent RBF, but not CBF. MBF therefore appears to be less sensitive than CBF to the magnitude of RSNA, but it is more able to respond to these higher frequencies of neural stimulation.
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Akeju, Oluwaseun, Kara J. Pavone, M. Brandon Westover, Rafael Vazquez, Michael J. Prerau, Priscilla G. Harrell, Katharine E. Hartnack, et al. "A Comparison of Propofol- and Dexmedetomidine-induced Electroencephalogram Dynamics Using Spectral and Coherence Analysis." Anesthesiology 121, no. 5 (November 1, 2014): 978–89. http://dx.doi.org/10.1097/aln.0000000000000419.
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Abstract Background Electroencephalogram patterns observed during sedation with dexmedetomidine appear similar to those observed during general anesthesia with propofol. This is evident with the occurrence of slow (0.1 to 1 Hz), delta (1 to 4 Hz), propofol-induced alpha (8 to 12 Hz), and dexmedetomidine-induced spindle (12 to 16 Hz) oscillations. However, these drugs have different molecular mechanisms and behavioral properties and are likely accompanied by distinguishing neural circuit dynamics. Methods The authors measured 64-channel electroencephalogram under dexmedetomidine (n = 9) and propofol (n = 8) in healthy volunteers, 18 to 36 yr of age. The authors administered dexmedetomidine with a 1-µg/kg loading bolus over 10 min, followed by a 0.7 µg kg−1 h−1 infusion. For propofol, the authors used a computer-controlled infusion to target the effect-site concentration gradually from 0 to 5 μg/ml. Volunteers listened to auditory stimuli and responded by button press to determine unconsciousness. The authors analyzed the electroencephalogram using multitaper spectral and coherence analysis. Results Dexmedetomidine was characterized by spindles with maximum power and coherence at approximately 13 Hz (mean ± SD; power, −10.8 ± 3.6 dB; coherence, 0.8 ± 0.08), whereas propofol was characterized with frontal alpha oscillations with peak frequency at approximately 11 Hz (power, 1.1 ± 4.5 dB; coherence, 0.9 ± 0.05). Notably, slow oscillation power during a general anesthetic state under propofol (power, 13.2 ± 2.4 dB) was much larger than during sedative states under both propofol (power, −2.5 ± 3.5 dB) and dexmedetomidine (power, −0.4 ± 3.1 dB). Conclusion The results indicate that dexmedetomidine and propofol place patients into different brain states and suggest that propofol enables a deeper state of unconsciousness by inducing large-amplitude slow oscillations that produce prolonged states of neuronal silence.
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Feld, Gordon B., Til O. Bergmann, Marjan Alizadeh-Asfestani, Viola Stuke, Jan-Philipp Wriede, Surjo Soekadar, and Jan Born. "Specific changes in sleep oscillations after blocking human metabotropic glutamate receptor 5 in the absence of altered memory function." Journal of Psychopharmacology 35, no. 6 (April 25, 2021): 652–67. http://dx.doi.org/10.1177/02698811211005627.
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Background: Sleep consolidates declarative memory by repeated replay linked to the cardinal oscillations of non-rapid eye movement (NonREM) sleep. However, there is so far little evidence of classical glutamatergic plasticity induced by this replay. Rather, we have previously reported that blocking N-methyl-D-aspartate (NMDA) or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors does not affect sleep-dependent consolidation of declarative memory. Aims: The aim of this study was to investigate the role of metabotropic glutamate receptor 5 (mGluR5) in memory processing during sleep. Methods: In two placebo-controlled within-subject crossover experiments with 20 healthy humans each, we used fenobam to block mGluR5 during sleep. In Experiment I, participants learned word-pairs (declarative task) and a finger sequence (procedural task) in the evening, then received the drug and recall was tested the next morning. To cover possible effects on synaptic renormalization processes during sleep, in Experiment II participants learned new word-pairs in the morning after sleep. Results/outcomes: Surprisingly, fenobam neither reduced retention of memory across sleep nor new learning after sleep, although it severely altered sleep architecture and memory-relevant EEG oscillations. In NonREM sleep, fenobam suppressed 12–15 Hz spindles but augmented 2–4 Hz delta waves, whereas in rapid eye movement (REM) sleep it suppressed 4–8 Hz theta and 16–22 Hz beta waves. Notably, under fenobam NonREM spindles became more consistently phase-coupled to the slow oscillation. Conclusions/interpretations: Our findings indicate that mGluR5-related plasticity is not essential for memory processing during sleep, even though mGlurR5 are strongly implicated in the regulation of the cardinal sleep oscillations.
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Destexhe, A., T. Bal, D. A. McCormick, and T. J. Sejnowski. "Ionic mechanisms underlying synchronized oscillations and propagating waves in a model of ferret thalamic slices." Journal of Neurophysiology 76, no. 3 (September 1, 1996): 2049–70. http://dx.doi.org/10.1152/jn.1996.76.3.2049.
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1. A network model of thalamocortical (TC) and thalamic reticular (RE) neurons was developed based on electrophysiological measurements in ferret thalamic slices. Single-compartment TC and RE cells included voltage- and calcium-sensitive currents described by Hodgkin-Huxley type of kinetics. Synaptic currents were modeled by kinetic models of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), gamma-aminobutyric acid-A (GABAA) and GABAB receptors. 2. The model reproduced successfully the characteristics of spindle and slow bicuculline-induced oscillations observed in vitro. The characteristics of these two types of oscillations depended on both the intrinsic properties of TC and RE cells and their pattern of interconnectivity. 3. The oscillations were organized by the reciprocal recruitment between TC and RE cells, due to their manual connectivity and bursting properties. TC cells elicited AMPA-mediated excitatory postsynaptic potentials (EPSPs) in RE cells, whereas RE cells elicited a mixture of GABAA and GABAB inhibitory postsynaptic potentials (IPSPs) in TC cells. Because of the presence of a T current, sufficiently strong EPSPs could elicit a burst in RE cells, and TC cells could generate a rebound burst following GABAergic IPSPs. Under these conditions, interaction between the TC and RE cells produced sustained oscillations. 4. In the absence of spontaneous oscillation in any cell, the TC-RE network remained quiescent. Spindle oscillations with a frequency of 9-11 Hz could be initiated by stimulation of either TC or RE neurons. A few spontaneously oscillating TC neurons recruited the entire network model into a "waxing-and waning" oscillation. These "initiator" cells could be an extremely small proportion of TC cells. 5. In intracellular recordings, TC cells display a reduced ability for burst firing after a sequence of bursts. The "waning" phase of spindles was reproduced in the network model by assuming an activity-dependent upregulation of Ih operating via a calcium-binding protein in TC cells, as shown previously in a two-cell model. 6. Following the global suppression of GABAA inhibition, the disinhibited RE cells produced prolonged burst discharges that elicited strong GABAB-mediated currents in TC cells. The enhancement of slow IPSPs in TC cells was also due to cooperativity in the activation of GABAB-mediated current. These slow IPSPs recruited TC and RE cells into slower waxing-and-waning oscillations (3-4 HZ) that were even more highly synchronized. 7. Local axonal arborization of the TC to RE and RE to TC projections allowed oscillations to propagate through the network. An oscillation starting at a single focus induced a propagating wavefront as more cells were recruited progressively. The waning of the oscillation also propagated due to upregulation of Ih in TC cells, leading to waves of spindle activity as observed in experiments. 8. The spatiotemporal properties of propagating waves in the model were highly dependent on the intrinsic properties of TC cells. The spatial pattern of spiking activity was markedly different for spindles compared with bicuculline-induced oscillations and depended on the rebound burst behavior of TC cells. The upregulation of Ih produced a refractory period so that colliding spindle waves merged into a single oscillation and extinguished. Finally, reducing the Ih conductance led to sustained oscillations. 9. Two key properties of cells in the thalamic network may account for the initiation, propagation, and termination of spindle oscillations, the activity-dependent upregulation of Ih in TC cells, and the localized axonal projections between TC and RE cells. In addition, the model predicts that a nonlinear stimulus dependency of GABAB responses accounts for the genesis of prolonged synchronized discharges following block of GABAA receptors.
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Yungher, Don A., Tiffany R. Morris, Valentina Dilda, James M. Shine, Sharon L. Naismith, Simon J. G. Lewis, and Steven T. Moore. "Temporal Characteristics of High-Frequency Lower-Limb Oscillation during Freezing of Gait in Parkinson’s Disease." Parkinson's Disease 2014 (2014): 1–7. http://dx.doi.org/10.1155/2014/606427.
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A cardinal feature of freezing of gait (FOG) is high frequency (3–8 Hz) oscillation of the legs, and this study aimed to quantify the temporal pattern of lower-body motion prior to and during FOG. Acceleration data was obtained from sensors attached to the back, thighs, shanks, and feet in 14 Parkinson’s disease patients performing timed-up-and-go tasks, and clinical assessment of FOG was performed by two experienced raters from video. A total of 23 isolated FOG events, defined as occurring at least 5 s after gait initiation and with no preceding FOG, were identified from the clinical ratings. The corresponding accelerometer records were analyzed within a 4 s window centered at the clinical onset of freezing. FOG-related high-frequency oscillation (an increase in power in the 3–8 Hz band >3 SD from baseline) followed a distal to proximal onset pattern, appearing at the feet, shanks, thighs, and then back over a period of 250 ms. Peak power tended to decrease as the focus of oscillation moved from feet to back. There was a consistent delay (mean 872 ms) between the onset of high frequency oscillation at the feet and clinical onset of FOG. We infer that FOG is characterized by high frequency oscillation at the feet, which progresses proximally and is mechanically damped at the torso.
Conference papers on the topic "4-8 Hz oscillation"
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Theodore, S., A. M. Al-Jumaily, and P. Mbikou. "Effect of Mechanical Pulse Oscillations on Pre-Contracted Porcine Airway Smooth Muscle." In ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-63154.
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This research focuses on investigating the effect of pulse oscillation rather than sinusoidal oscillation on contracted airway smooth muscle (ASM). Isolated ASM were tested using pulse oscillations with Frequency of 0.5 Hz, 1Hz and 2Hz; Amplitude of 2%, 4%, 6% and 8%, and duration of 1 min, 2 min and 3 min (n = 5). Results obtained from the experiments showed that pulse oscillation with short duration had significant effect on the relaxation of ASM compared to sinusoidal oscillations with longer duration.
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Baek, Seung Il, and Savas Yavuzkurt. "Effects of Oscillations in the Mainstream on Film Cooling at Various Blowing Ratios." In ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/gt2017-63398.
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The objective of this study is to understand the effects of flow oscillations in the mainstream and film cooling jets on film cooling at various blowing ratios (0.5, 0.78, 1.0 and 1.5). These oscillations could be caused by the combustion instabilities. They are approximated in sinusoidal form for the current study. The effects of different frequencies (0, 2, 16, 32 Hz) on film cooling are investigated. Simulations are performed using URANS Realizable k-epsilon and LES Smagorinsky-Lilly turbulence models. The results indicate that if the frequencies of the mainstream and the jet flow are increased at a low average blowing ratio of M = 0.5, the adiabatic film cooling effectiveness is decreased and the heat transfer coefficient is increased due to increased disturbance in jet and main flow interaction with increasing frequency. It was observed that when the frequency of the mainstream and the cooling jet flow is increased at M = 0.5, the amplitude of the pressure difference between the mainstream and the plenum is increased resulting in increased amplitude of coolant flow rate oscillations leading to more jet lift off and more disturbance in the main flow and coolant interaction. Consequently, adiabatic film cooling effectiveness is decreased and heat transfer coefficient is increased. If the frequency of the mainstream is increased from 0 Hz to 2, 16, or 32 Hz at M = 0.5, the centerline effectiveness is decreased about 10%, 12%, or 47% and the spanwise-averaged Stanton number ratio is increased about 4%, 5%, or 9% respectively. If the frequencies of the main flow and the jet flow are increased at higher blowing ratios of M = 1.0 and 1.5, adiabatic effectiveness is increased and the spanwise-averaged heat transfer coefficient are decreased. Under steady flow conditions jet lift off is generated for these high blowing ratios. If the frequency of the mainstream and the jet flow is increased, the amplitude of coolant jet flow rate oscillation is increased for the same reason as mentioned above for M = 0.5. This leads to less jet lift off during the cycle resulting in more frequent coolant contact with the wall and consequently increased centerline effectiveness as frequency increases. In addition, the entrainment of hot gases underneath the jet doesn’t lead to higher mixing between the hot mainstream and the coolant and this results in decreased heat transfer coefficient. This is also indicated by the turbulent kinetic energy levels. Some representative results are: when the frequency of the main flow is increased from 0 Hz to 2, 16, or 32 Hz at M = 1.0, the centerline effectiveness is increased about 8%, 19%, or 320%. Also, if the oscillation frequency is increased from 2 Hz to 16, or 32 Hz at M = 1.0, the spanwise-averaged Stanton number ratio is decreased around 2%, to 5% respectively. It seems like the cut off point for low and high blowing ratio behavior of cooling jets is around M = 0.78.
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De Barnier, Thibaud, and Mickael Causse. "Can Vigilance be Enhanced by Flashing Visual Stimuli? An EEG Study." In 13th International Conference on Applied Human Factors and Ergonomics (AHFE 2022). AHFE International, 2022. http://dx.doi.org/10.54941/ahfe1001579.
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In aviation, poor vigilance has been cited as an important factor of incidents and accidents. Consequently, many studies are conducted in order to detect the level of vigilance and thus reduce the risk of occurrence of low task engagement or low awareness. Being able to enhance someone’s level of vigilance could be useful in many fields, such as aviation or the navy, in particular when a particularly high level of awareness is required (critical maneuvers, occurrence of warning alarms etc.). With the evolution of the knowledge about brain waves, it seems now possible to influence cortical activity by inducing specific wave patterns, using stimuli such as binaural sounds or visual flashes. In this study, we assessed the possibility of artificially increasing the level of vigilance by stimulating brain activity using flashing visual stimuli. Twelve participants performed a vigilance test (Mackworth clock test) while visual flashing stimuli were displayed around the task on the screen border, and at different flashing frequencies (0 Hz, 4 Hz, 8 Hz, 40 Hz). Brain waves were recorded continuously with a 32-channel electroencephalogram (EEG). Results revealed that reaction times during the vigilance task were shorter with the 40 Hz flashing stimuli. However, subjective mental workload was increased by the presence of each type of visual flash. With the 40 Hz flash, gamma activity (roughly oscillating to the frequency of the 40 Hz flash) in the visual cortex was much higher than with the other flashing frequencies. Interestingly, this increased gamma activity was extended to the frontal regions. In addition, the theta/beta ratio was generally higher on frontal electrodes with lower flashing frequency (4 Hz) than with faster flashing frequencies (8 Hz and 40 Hz). It suggests that the vigilance level was poorer with lower flashing frequency. Indeed, higher theta/beta ratio has been associated with lower vigilance levels and mind wandering episodes. Despite these rather encouraging results, replications of such studies are needed to confirm that visual flashing stimuli can modulate vigilance level and elicit specific brain waves, in particular in regions outside the visual cortex.
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Aktas, Engin, Mark Seaver, Jonathan M. Nichols, and Stephen T. Trickey. "Quantitative Detection of Low Energy Impact Damage in a Sandwich Composite UAV Wing." In ASME 2008 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. ASMEDC, 2008. http://dx.doi.org/10.1115/smasis2008-327.
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This work describes damage detection efforts applied to a foam core composite wing following a series of low energy impacts in adjacent locations. The wing is a sandwich composite, composed of 4 layers of woven carbon fiber fabric surrounding a short aluminum core in the center (where it’s connected to the fuselage) and a foam core for the outer portions of the wing. The wing measures 1320 mm. × 152.4 mm. × 13.4 mm and has an airfoil cross-section. Thirteen impacts (6 – 8 J deposited energy) were applied at adjacent locations approximately 1/3 of the way out from the center. Following one or two impacts, the wing was tested using static tip deflection and dynamic vibrational excitation. Static and dynamic strains were measured using 8 fiber Bragg grating (FBG) sensors. Dynamic acceleration was also monitored using 3 conventional accelerometers. Dynamic excitation included the output of a Lorenz oscillator (0 – ∼150 Hz), simulated gust loading (0 – 150 Hz), and Gaussian white noise (0 – 1500 Hz). The analysis is a quantitative assessment of response nonlinearity based on the assumption that the undamaged wing behaves linearly and that the damage introduces nonlinearity into the vibrational response.