To see the other types of publications on this topic, follow the link: Aperiodic activity.
Journal articles on the topic 'Aperiodic activity'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'Aperiodic activity.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Freeman, W. J. "A proposed name for aperiodic brain activity: stochastic chaos." Neural Networks 13, no. 1 (January 2000): 11–13. http://dx.doi.org/10.1016/s0893-6080(99)00093-3.
Full text
2
Smith, Myron A. "Recent Spectroscopic Evidence for Aperiodic Activity in Classical Be Stars." International Astronomical Union Colloquium 175 (2000): 292–303. http://dx.doi.org/10.1017/s0252921100056049.
Full textAbstract:
AbstractThis review focuses on aperiodic line profile activity in several Be stars, ignoring attributes of pulsations probably occurring in any of the stars studied. Herein, I discuss spectroscopic evidence of heating (and cooling) of regions of Be star atmospheres, of line profile transients called dimples and high velocity absorptions. These features will be interpreted in terms of mass ejections (not necessarily permanent). Some of these events are violent and spasmodic, some are ordered and quasisteady, and some are associated with downflows. I close with new evidence for time-varying, corotating clouds suspended over a few Be stars.
3
Varner, K. J., S. M. Barman, and G. L. Gebber. "Cat diencephalic neurons with sympathetic nerve-related activity." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 254, no. 2 (February 1, 1988): R257—R267. http://dx.doi.org/10.1152/ajpregu.1988.254.2.r257.
Full textAbstract:
In a companion paper, we demonstrated that hypothalamic or medial thalamic lesions attenuate the reduction in inferior cardiac postganglionic sympathetic nerve discharge (SND) produced by decerebration in the anesthetized cat [Huang et al., Am. J. Physiol. 254 (Regulatory Integrative Comp. Physiol. 23): R249-R256, 1988]. This raised the possibility that these diencephalic regions contain the cell bodies of neurons that contribute to SND. The current study tested this possibility in cats anesthetized with alpha-chloralose. Spike-triggered averaging of inferior cardiac SND revealed the existence of two types of hypothalamic and medial thalamic neurons with sympathetic nerve-related activity. Recordings were made from the soma-dendritic region of these neurons, since an inflection often appeared on the rising phase of the unit action potential. The activity of type 1 neurons was synchronized to an aperiodic spikelike event in SND, whereas that of type 2 neurons was synchronized to a 2- to 6-Hz rhythmic component. Some of the type 2 neurons but none of the type 1 neurons had cardiac-related activity. Microstimulation at type 1 and type 2 unit recording sites increased SND. Our results are consistent with the possibility that hypothalamic and medial thalamic neurons contribute to the rhythmic and aperiodic components of SND in the anesthetized cat.
4
Donoghue, Thomas, Julio Dominguez, and Bradley Voytek. "Electrophysiological Frequency Band Ratio Measures Conflate Periodic and Aperiodic Neural Activity." eneuro 7, no. 6 (September 25, 2020): ENEURO.0192–20.2020. http://dx.doi.org/10.1523/eneuro.0192-20.2020.
Full text
5
Ishizuka, Kentaro, Tomohiro Nakatani, Masakiyo Fujimoto, and Noboru Miyazaki. "Noise robust voice activity detection based on periodic to aperiodic component ratio." Speech Communication 52, no. 1 (January 2010): 41–60. http://dx.doi.org/10.1016/j.specom.2009.08.003.
Full text
6
Ramsay, Ian, Peter Lynn, Erik Lee, Brandon Schermitzler, David Leipold, and Scott Sponheim. "Disturbances in Aperiodic Neural Activity During Resting State in Patients With Schizophrenia." Biological Psychiatry 89, no. 9 (May 2021): S254—S255. http://dx.doi.org/10.1016/j.biopsych.2021.02.637.
Full text
7
Katz, J. I. "Testing models of periodically modulated FRB activity." Monthly Notices of the Royal Astronomical Society 502, no. 3 (February 11, 2021): 4664–68. http://dx.doi.org/10.1093/mnras/stab399.
Full textAbstract:
ABSTRACT The activity of the repeating FRB 20180916B is periodically modulated with a period of 16.3 d, and FRB 121102 may be similarly modulated with a period of about 160 d. In some models of this modulation, the period derivative is insensitive to the uncertain parameters; these models can be tested by measurement of or bounds on the derivative. In other models, values of the uncertain parameters can be constrained. Periodic modulation of aperiodic bursting activity may result from emission by a narrow beam wandering within a cone or funnel along the axis of a precessing disc, such as the accretion discs in X-ray binaries. The production of FRB 200428 by a neutron star that is neither accreting nor in a binary then shows universality: coherent emission occurring in a wide range of circumstances.
8
Sheeba, V., M. Chandrashekaran, Amitabh Joshi, and Vijay Sharma. "Locomotor activity rhythm in Drosophila melanogaster after 600 generations in an aperiodic environment." Naturwissenschaften 89, no. 11 (November 1, 2002): 512–14. http://dx.doi.org/10.1007/s00114-002-0360-9.
Full text
9
Singer, Annabelle C., Giovanni Talei Franzesi, Suhasa B. Kodandaramaiah, Francisco J. Flores, Jeremy D. Cohen, Albert K. Lee, Christoph Borgers, Craig R. Forest, Nancy J. Kopell, and Edward S. Boyden. "Mesoscale-duration activated states gate spiking in response to fast rises in membrane voltage in the awake brain." Journal of Neurophysiology 118, no. 2 (August 1, 2017): 1270–91. http://dx.doi.org/10.1152/jn.00116.2017.
Full textAbstract:
We analyzed subthreshold activity preceding spikes in hippocampus and barrel cortex of awake mice. Aperiodic voltage ramps extending over tens to hundreds of milliseconds consistently precede and facilitate spikes, in a manner dependent on both their amplitude and their duration. These voltage ramps represent a “mesoscale” activated state that gates spike production in vivo.
10
Silbert, B. S., E. Koumoundouros, M. J. Davies, and K. D. Cronin. "The use of Aperiodic Analysis of the EEG during Carotid Artery Surgery." Anaesthesia and Intensive Care 17, no. 1 (February 1989): 16–23. http://dx.doi.org/10.1177/0310057x8901700105.
Full textAbstract:
A new processed EEG machine, the Lifescan, ® which uses aperiodic analysis, was used to monitor cerebral activity prospectively in twenty-one patients undergoing carotid artery surgery under general anaesthesia. The machine was easy to apply, use and read. Volatile agents caused a bilateral decrease in high frequency activity. Unilateral changes consistent with cerebral ischaemia at the time of carotid cross-clamping were also seen. One such prolonged change was not associated with neurological deficit. A further patient awoke with neurological deficit without displaying Lifescan® evidence of ischaemia. The machine requires further assessment.
11
Goh, Grace, Shane Maloney, Peter Mark, and Dominique Blache. "Episodic Ultradian Events—Ultradian Rhythms." Biology 8, no. 1 (March 14, 2019): 15. http://dx.doi.org/10.3390/biology8010015.
Full textAbstract:
In the fast lane of chronobiology, ultradian events are short-term rhythms that have been observed since the beginning of modern biology and were quantified about a century ago. They are ubiquitous in all biological systems and found in all organisms, from unicellular organisms to mammals, and from single cells to complex biological functions in multicellular animals. Since these events are aperiodic and last for a few minutes to a few hours, they are better classified as episodic ultradian events (EUEs). Their origin is unclear. However, they could have a molecular basis and could be controlled by hormonal inputs—in vertebrates, they originate from the activity of the central nervous system. EUEs are receiving increasing attention but their aperiodic nature requires specific sampling and analytic tools. While longer scale rhythms are adaptations to predictable changes in the environment, in theory, EUEs could contribute to adaptation by preparing organisms and biological functions for unpredictability.
12
Satinoff, E., H. Li, T. K. Tcheng, C. Liu, A. J. McArthur, M. Medanic, and M. U. Gillette. "Do the suprachiasmatic nuclei oscillate in old rats as they do in young ones?" American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 265, no. 5 (November 1, 1993): R1216—R1222. http://dx.doi.org/10.1152/ajpregu.1993.265.5.r1216.
Full textAbstract:
The basis of the decline in circadian rhythms with aging was addressed by comparing the patterns of three behavioral rhythms in young and old rats with the in vitro rhythm of neuronal activity in the suprachiasmatic nuclei (SCN), the primary circadian pacemaker. In some old rats, rhythms of body temperature, drinking, and activity retained significant 24-h periodicities in entraining light-dark cycles; in others, one or two of the rhythms became aperiodic. When these rats were 23-27.5 mo old they were killed, and single-unit firing rates in SCN brain slices were recorded continuously for 30 h. There was significant damping of mean peak neuronal firing rates in old rats compared with young. SCN neuronal activities were analyzed with reference to previous entrained behavioral rhythm patterns of individual rats as well. Neuronal activity from rats with prior aperiodic behavioral rhythms was erratic, as expected. Neuronal activity from rats that were still maintaining significant 24-h behavioral rhythmicity at the time they were killed was erratic in most cases but normally rhythmic in others. Thus there was no more congruence between the behavioral rhythms and the brain slice rhythms than there was among the behavioral rhythms alone. These results, the first to demonstrate aberrant SCN firing patterns and a decrease in amplitude in old rats, imply that aging could either disrupt coupling between SCN pacemaker cells or their output, or cause deterioration of the pacemaking properties of SCN cells.
13
Karlsson, Karl Æ., and Mark S. Blumberg. "Temperature-Induced Reciprocal Activation of Hippocampal Field Activity." Journal of Neurophysiology 91, no. 1 (January 2004): 583–88. http://dx.doi.org/10.1152/jn.00953.2003.
Full textAbstract:
Hippocampal network activity oscillates between sustained rhythms (e.g., theta) and aperiodic population spikes (e.g., sharp waves, dentate spikes). Although temperature is known to modulate various aspects of rhythmic hippocampal activity, little is known regarding the influence of temperature on the incidence of population spikes. We recorded spontaneous hippocampal activity along the CA1-dentate gyrus axis using multisite silicon electrodes in urethanized infant rats (P2-P16) at brain temperatures of 37 and 27°C. Theta and gamma activity, as well as sharp waves, were detected at 37°C but not at 27°C. In contrast, dentate spikes were rare at 37°C but their incidence increased several-fold at 27°C (epileptiform activity also emerged at 27°C in the oldest pups). This surprising increase in the incidence of dentate spike activity in a cold brain represents the first such demonstration for a neuronal field pattern. In addition, these findings indicate that changes in brain temperature produce systems-level shifts in the balance among reciprocally interacting hippocampal components.
14
Leyk, Gisela, and Wolfgang Martin. "Latitude Dependent Circadian Rhythms of Carabid Beetles." Zeitschrift für Naturforschung C 41, no. 9-10 (October 1, 1986): 935–45. http://dx.doi.org/10.1515/znc-1986-9-1021.
Full textAbstract:
Abstract Comparative studies of circadian activity rhythms were performed with three stocks of the species Pterostichus rhaeticus Heer (from Southern Europe, Central Europe, and the Subarctic) and with one Central European stock of the sibling species Pterostichus nigrita Paykull. The hehaviour was investigated in various LD conditions, constant conditions including LL with changes of the illumination intensity and constant darkness with light pulses. The data were analysed with the program system “Timesdia” containing various techniques like power spectrum estimation, periodogram analysis and complex demodulation. This allowed to reveal the time course of rhythms and to determine the number of phase jumps as a measure for precision. With the help of these methods, the activity patterns are classified in different types of behaviour: synchronization, temporarily synchronization, aperiodic behaviour, free run, temporarily free run, relative entrainment, and relative coordination. Besides graduated differences between the populations in south-to-north direction (e.g. in the tendency to rhythmic behaviour) the analysis revealed splitting of rhythms into two or even three components of different frequencies and transitions from rhythmic to aperiodic behaviour or vice versa after arbitrarily chosen light pulses in constant darkness. This behaviour cannot be explained by a system which is composed of one single limit cycle oscillator, but the results rather support a multi-oscillator model.
15
Shefov, N. N., and A. I. Semenov. "Spectral composition of the cyclic aperiodic (quasibiennial) variations in solar activity and the Earth’s atmosphere." Geomagnetism and Aeronomy 46, no. 4 (July 2006): 411–16. http://dx.doi.org/10.1134/s0016793206040013.
Full text
16
LORENZO, M. NIEVES, NOELIA MONTEJO, VICENTE PÉREZ-MUÑUZURI, and VICENTE PÉREZ-VILLAR. "GLOBAL AND LOCAL NOISE ON DIFFUSIVELY COUPLED NEURAL NETWORKS." Fluctuation and Noise Letters 04, no. 04 (December 2004): R57—R65. http://dx.doi.org/10.1142/s0219477504002154.
Full textAbstract:
In this paper the effect of noise on activity of a neural network of diffusively coupled excitatory-inhibitory cells with time delay is analyzed. We distinguish between global and local noise studying the different types of spatiotemporal behaviors observed when a space-time correlated noise is applied to the system. The results show a synchronization of the network in aperiodic behavior with the help of tiny noisy perturbations on the external signal depending on the spatial correlation of noise and the coupling coefficients.
17
Usher, Marius, Heinz Georg Schuster, and Ernst Niebur. "Dynamics of Populations of Integrate-and-Fire Neurons, Partial Synchronization and Memory." Neural Computation 5, no. 4 (July 1993): 570–86. http://dx.doi.org/10.1162/neco.1993.5.4.570.
Full textAbstract:
We study the dynamics of completely connected populations of refractory integrate-and-fire neurons in the presence of noise. Solving the master equation based on a mean-field approach, and by computer simulations, we find sustained states of activity that correspond to fixed points and show that for the same value of external input, the system has one or two attractors. The dynamic behavior of the population under the influence of external input and noise manifests hysteresis effects that might have a functional role for memory. The temporal dynamics at higher temporal resolution, finer than the transmission delay times and the refractory period, are characterized by synchronized activity of subpopulations. The global activity of the population shows aperiodic oscillations analogous to experimentally found field potentials.
18
FREEMAN, WALTER J. "NOISE-INDUCED FIRST-ORDER PHASE TRANSITIONS IN CHAOTIC BRAIN ACTIVITY." International Journal of Bifurcation and Chaos 09, no. 11 (November 1999): 2215–18. http://dx.doi.org/10.1142/s0218127499001656.
Full textAbstract:
Brain electrical activity in animals during normal behaviors has aperiodic wave forms suggesting its origin in chaotic dynamics. Attempts at finding experimental proofs using low-dimensional, deterministic chaotic models have not succeeded. The assumptions of autonomy, stationarity,and noise-free operation that are needed to define these at tractors and their embedding dimensions have been shown not to hold for brains, because numerical estimates of correlation dimensions and Lyapunov exponents have failed to converge to normative values. Analysis of EEGs from sensory cortices show that a very different model applies to brains, which is more closely related to lasers than models of twist–flip maps and reaction–diffusion systems. Neurons interact with each other through channels with nonlinear, amplitude-dependent gains, by which they form fields of white noise. When the strengths of interaction are increased by input from receptors, the neurons interact more strongly and lose their high degrees of freedom. The macroscopic constraint on their activity appears as an order parameter in the form of spatially coherent, indeterministic chaos.
19
Higgs, Matthew H., and Charles J. Wilson. "Unitary synaptic connections among substantia nigra pars reticulata neurons." Journal of Neurophysiology 115, no. 6 (June 1, 2016): 2814–29. http://dx.doi.org/10.1152/jn.00094.2016.
Full textAbstract:
Neurons in substantia nigra pars reticulata (SNr) are synaptically coupled by local axon collaterals, providing a potential mechanism for local signal processing. Because SNr neurons fire spontaneously, these synapses are constantly active. To investigate their properties, we recorded spontaneous inhibitory postsynaptic currents (sIPSCs) from SNr neurons in brain slices, in which afferents from upstream nuclei are severed, and the cells fire rhythmically. The sIPSC trains contained a mixture of periodic and aperiodic events. Autocorrelation analysis of sIPSC trains showed that a majority of cells had one to four active unitary inputs. The properties of the unitary IPSCs (uIPSCs) were analyzed for cells with one unitary input, using a model of periodic presynaptic firing and stochastic synaptic transmission. The inferred presynaptic firing rates and coefficient of variation of interspike intervals (ISIs) corresponded well with direct measurements of spiking in SNr neurons. Methods were developed to estimate the success probability, amplitude distributions, and kinetics of the uIPSCs, while removing the contribution from aperiodic sIPSCs. The sIPSC amplitudes were not increased upon release from halorhodopsin silencing, suggesting that most synapses were not depressed at the spontaneous firing rate. Gramicidin perforated-patch recordings indicated that the average reversal potential of spontaneous inhibitory postsynaptic potentials was −64 mV. Because of the change in driving force across the ISI, the unitary inputs are predicted to have a larger postsynaptic impact when they arrive late in the ISI. Simulations of network activity suggest that this very sparse inhibitory coupling may act to desynchronize the activity of SNr neurons while having only a small effect on firing rate.
20
Schaworonkow, Natalie, and Bradley Voytek. "Longitudinal changes in aperiodic and periodic activity in electrophysiological recordings in the first seven months of life." Developmental Cognitive Neuroscience 47 (February 2021): 100895. http://dx.doi.org/10.1016/j.dcn.2020.100895.
Full text
21
Wolfrom, C., N. P. Chau, J. Maigne, J. C. Lambert, B. Ducot, S. Guerroui, and J. Deschatrette. "Evidence for deterministic chaos in aperiodic oscillations of proliferative activity in long-term cultured Fao hepatoma cells." Journal of Cell Science 113, no. 6 (March 15, 2000): 1069–74. http://dx.doi.org/10.1242/jcs.113.6.1069.
Full textAbstract:
The proliferative activity of long-term cultured mammalian cells exhibits traits of a complex dynamic system, with a succession of spontaneous rises and falls in proliferation rate. We analyzed three successive series of proliferation data for the Fao hepatoma cell line in long-term cultures. In the three series the proliferation rate displayed apparently disordered oscillations, which each lasted about 3–5 passages, with variable amplitude and were therefore unpredictable. Such non-linear kinetics raises the major issue of whether these fluctuations are random, or determined and coordinated. We used a graphical method of analysis of the data, which demonstrated that all troughs of proliferation were mathematically related to a common value in each series. This common value was itself related to the maximum level of proliferation of the cell line. Non-linear analysis thus confirmed that the fluctuations in proliferation rate of tumoral Fao cells are, at least in part, determined. This pattern evokes chaotic dynamics and is evidence for the flexible coordination of the complex system linking positive and negative growth regulators in long-term cultured cells.
22
Kim, Jung-Ho, Hyung-Hwa Ko, and Chul-Ho Kang. "A Study on Voice Activity Detection Using Auditory Scene and Periodic to Aperiodic Component Ratio in CASA System." Journal of the Institute of Electronics and Information Engineers 50, no. 10 (October 25, 2013): 181–87. http://dx.doi.org/10.5573/ieek.2013.50.10.181.
Full text
23
Lim, S. H., N. Phonthammachai, T. Liu, and T. J. White. "X-ray absorption spectroscopy studies of phase transformations and amorphicity in nanotitania powder and silica–titania core–shell photocatalysts." Journal of Applied Crystallography 41, no. 6 (November 11, 2008): 1009–18. http://dx.doi.org/10.1107/s0021889808032718.
Full textAbstract:
The local environment of titanium in nanocrystalline sol-gel synthesized titania, cobaltiferous titania and silica–titania core–shell photocatalysts was investigated using X-ray absorption spectroscopy (XAS). Anatase reconstructively transforms to rutileviaa persistent amorphous phase that is retained, in part, up to 1273 K. In nanotitania, temperature-dependent trends in Ti order correlation observed by XAS parallel the development of amorphous content extracted from powder X-ray diffraction patterns, such that amorphicity shows a transient maximum at ∼873 K with the onset of rutile crystallization. Cobaltiferous and core–shell materials behaved similarly, but with anatase retained to 973 and 1273 K, respectively. In the former, cobalt redox reactions may stabilize anatase to higher temperatures by ready charge-balancing during the loss of hydroxyl and the formation of oxygen vacancies. In the core–shell architecture, higher Ti coordination and interatomic distance variance in the first- and second-nearest-neighbour shells are maintained to 1273 K by interaction of a substantially aperiodic TiO6network with the glassy silica substrate, which inhibits crystallization of rutile from the amorphous intermediate. Comparisons are also drawn with the commercial P25 catalyst. The overall transformation mechanism can be summarized as gel → non-stoichiometric anatase → amorphous titania → rutile. Smaller anatase crystals and a higher average Ti—Ti coordination environment in the core–shell structure may enhance photocatalytic activity directly, by creating larger specific surface areas and hosting reactive defects, or indirectly, by inhibiting exciton annihilation in aperiodic titania and delaying the crystallization of less photoactive rutile.
24
Renout, Karen A., Herbert A. Leeper, Donna L. Bandur, and Arthur J. Hudson. "Vocal Fold Diadochokinetic Function of Individuals With Amyotrophic Lateral Sclerosis." American Journal of Speech-Language Pathology 4, no. 1 (February 1995): 73–80. http://dx.doi.org/10.1044/1058-0360.0401.73.
Full textAbstract:
This study relates over time the changes in voluntary opening and closing of the vocal folds (vocal fold diadochokinesis, or VFDDK) of patients with amyotrophic lateral sclerosis (ALS). The rate, pattern, and periodicity of VFDDK were examined for 12 ALS subjects with bulbar and 14 subjects with nonbulbar signs of the disease. The acoustical data were analyzed with a commercially available computer-based speech analysis system. ALS patients with bulbar and nonbulbar symptoms demonstrate reduced rate and aperiodic VFDDK as the symptomatology of the neuromotor system progresses. Individuals with bulbar signs show a greater change in vocal fold activity than do the nonbulbar group. Discussion of the clinical implications for initial diagnosis and monitoring of changes over time in motor control of laryngeal function is presented.
25
Chang, Hung-Jen, Walter J. Freeman, and Brian C. Burke. "Biologically Modeled Noise Stabilizing Neurodynamics for Pattern Recognition." International Journal of Bifurcation and Chaos 08, no. 02 (February 1998): 321–45. http://dx.doi.org/10.1142/s021812749800019x.
Full textAbstract:
We present a distributed KIII model for the olfactory neural system. Low-level Gaussian noise is introduced to the receptors and anterior olfactory nucleus, which biologically models the peripheral and central sources of noise. The additive noise numerically makes the model stable and robust in respect to repeated input-induced state transitions, while improving the simulations of EEG potentials and multiunit activity from the olfactory system. This hybrid dynamics generates a 1/f aperiodic state, which provides an unpatterned basal state for every module to stay in while there is no significant stimulus. Any external input may guide the system to a certain patterned state. The mechanism is fast, fully parallel, under modulatory control, and flexible in absorbing new patterns from unpredictable environments.
26
Eracleous, M., K. Horne, M. Livio, and W. F. Welsh. "The Flares of AE Aqr." International Astronomical Union Colloquium 158 (1996): 165–66. http://dx.doi.org/10.1017/s0252921100038513.
Full textAbstract:
AbstractThe enigmatic flaring activity of AE Aqr, which extends from the radio to the X-ray bands, may be the exotic outcome of a relatively feeble accretion flow onto the rapidly spinning white dwarf. We summarize and interpret the results of recent observations by HST and ROSAT of the aperiodic flares. Optical and UV flares are tightly correlated and are clearly involved in powering the emission lines. The spectrum of a flare consists of a Balmer continuum, and a plethora of emission lines, which vary synchronously. The large optical/UV flares are not accompanied by large X-ray outbursts. The radial velocity curves of the UV lines, and of Hα, suggest that they originate in the accretion stream. The observational results dis-favor scenarios invoking coronal activity on the secondary star or instabilities at the disk/magnetosphere interface. Rather, they support a recently proposed scenario in which the accretion flow consists of blobs which are shocked upon encountering the white dwarf magnetosphere.
27
Dorval, Alan D., Alexis M. Kuncel, Merrill J. Birdno, Dennis A. Turner, and Warren M. Grill. "Deep Brain Stimulation Alleviates Parkinsonian Bradykinesia by Regularizing Pallidal Activity." Journal of Neurophysiology 104, no. 2 (August 2010): 911–21. http://dx.doi.org/10.1152/jn.00103.2010.
Full textAbstract:
Deep brain stimulation (DBS) of the basal ganglia can alleviate the motor symptoms of Parkinson's disease although the therapeutic mechanisms are unclear. We hypothesize that DBS relieves symptoms by minimizing pathologically disordered neuronal activity in the basal ganglia. In human participants with parkinsonism and clinically effective deep brain leads, regular (i.e., periodic) high-frequency stimulation was replaced with irregular (i.e., aperiodic) stimulation at the same mean frequency (130 Hz). Bradykinesia, a symptomatic slowness of movement, was quantified via an objective finger tapping protocol in the absence and presence of regular and irregular DBS. Regular DBS relieved bradykinesia more effectively than irregular DBS. A computational model of the relevant neural structures revealed that output from the globus pallidus internus was more disordered and thalamic neurons made more transmission errors in the parkinsonian condition compared with the healthy condition. Clinically therapeutic, regular DBS reduced firing pattern disorder in the computational basal ganglia and minimized model thalamic transmission errors, consistent with symptom alleviation by clinical DBS. However, nontherapeutic, irregular DBS neither reduced disorder in the computational basal ganglia nor lowered model thalamic transmission errors. Thus we show that clinically useful DBS alleviates motor symptoms by regularizing basal ganglia activity and thereby improving thalamic relay fidelity. This work demonstrates that high-frequency stimulation alone is insufficient to alleviate motor symptoms: DBS must be highly regular. Descriptive models of pathophysiology that ignore the fine temporal resolution of neuronal spiking in favor of average neural activity cannot explain the mechanisms of DBS-induced symptom alleviation.
28
Kibombo, Harrison S., Shivatharsiny Rasalingam, and Ranjit T. Koodali. "Facile template free method for textural property modulation that enhances adsorption and photocatalytic activity of aperiodic titania supported silica materials." Applied Catalysis B: Environmental 142-143 (October 2013): 119–28. http://dx.doi.org/10.1016/j.apcatb.2013.05.020.
Full text
29
Honma, Sato, Nobue Kanematsu, Yumiko Katsuno, and Ken-ichi Honma. "Persistence of circadian oscillation while locomotor activity and plasma melatonin levels became aperiodic under prolonged continuous light in the rat." Neuroscience Letters 216, no. 1 (September 1996): 49–52. http://dx.doi.org/10.1016/0304-3940(96)13006-8.
Full text
30
Олексій Чорний, Лариса Герасименко, and Віктор Бушер. "МОДЕЛЮВАННЯ ПРОЦЕСУ НАУЧІННЯ НА ОСНОВІ ВИКОРИСТАННЯ ДИФЕРЕНЦІАЛЬНИХ РІВНЯНЬ ДРОБОВИХ ПОРЯДКІВ." World Science 3, no. 5(57) (May 31, 2020): 10–19. http://dx.doi.org/10.31435/rsglobal_ws/31052020/7083.
Full textAbstract:
This article is an integrated study conducted to develop a learning model which would make it possible to identify the students' changes of knowledge, abilities and skills acquisition over time as well as the formation of special features of their individual background. The authors have demonstrated how the traditional system of students' learning and cognitive activity management can be improved. Also, they have justified the application of the cybernetic model based on fractional equations for the description and evaluation of the student's learning process. As a result of the findings, students who assimilate the content of teaching information and form personal experience in different ways have compiled different groups; the learning curve constructed on the basis of the heterogeneous differential equation of second order with integer powers has been compared with the set of models with equations of fractional order of aperiodic and fractional power components.
31
Zhao, Zihan, Xuejiao Xu, Hairong Cheng, Michelle C. Miller, Zhen He, Hongming Gu, Zhongyu Zhang, et al. "Galectin-3 N-terminal tail prolines modulate cell activity and glycan-mediated oligomerization/phase separation." Proceedings of the National Academy of Sciences 118, no. 19 (May 5, 2021): e2021074118. http://dx.doi.org/10.1073/pnas.2021074118.
Full textAbstract:
Galectin-3 (Gal-3) has a long, aperiodic, and dynamic proline-rich N-terminal tail (NT). The functional role of the NT with its numerous prolines has remained enigmatic since its discovery. To provide some resolution to this puzzle, we individually mutated all 14 NT prolines over the first 68 residues and assessed their effects on various Gal-3–mediated functions. Our findings show that mutation of any single proline (especially P37A, P55A, P60A, P64A/H, and P67A) dramatically and differentially inhibits Gal-3–mediated cellular activities (i.e., cell migration, activation, endocytosis, and hemagglutination). For mechanistic insight, we investigated the role of prolines in mediating Gal-3 oligomerization, a fundamental process required for these cell activities. We showed that Gal-3 oligomerization triggered by binding to glycoproteins is a dynamic process analogous to liquid–liquid phase separation (LLPS). The composition of these heterooligomers is dependent on the concentration of Gal-3 as well as on the concentration and type of glycoprotein. LLPS-like Gal-3 oligomerization/condensation was also observed on the plasma membrane and disrupted endomembranes. Molecular- and cell-based assays indicate that glycan binding–triggered Gal-3 LLPS (or LLPS-like) is driven mainly by dynamic intermolecular interactions between the Gal-3 NT and the carbohydrate recognition domain (CRD) F-face, although NT–NT interactions appear to contribute to a lesser extent. Mutation of each proline within the NT differentially controls NT–CRD interactions, consequently affecting glycan binding, LLPS, and cellular activities. Our results unveil the role of proline polymorphisms (e.g., at P64) associated with many diseases and suggest that the function of glycosylated cell surface receptors is dynamically regulated by Gal-3.
32
Sidoli, Lara, Konstantin A. Postnov, Andrea Belfiore, Martino Marelli, David Salvetti, Ruben Salvaterra, Andrea De Luca, and Paolo Esposito. "Supergiant Fast X-ray Transients uncovered by the EXTraS project: flares reveal the development of magnetospheric instability in accreting neutron stars." Monthly Notices of the Royal Astronomical Society 487, no. 1 (May 10, 2019): 420–34. http://dx.doi.org/10.1093/mnras/stz1283.
Full textAbstract:
ABSTRACT The low luminosity, X-ray flaring activity, of the sub-class of high-mass X-ray binaries called Supergiant Fast X-ray Transients, has been investigated using XMM–Newton public observations, taking advantage of the products made publicly available by the EXTraS project. One of the goals of EXTraS was to extract from the XMM–Newton public archive information on the aperiodic variability of all sources observed in the soft X-ray range with EPIC (0.2–12 keV). Adopting a Bayesian block decomposition of the X-ray light curves of a sample of SFXTs, we picked out 144 X-ray flares, covering a large range of soft X-ray luminosities (1032–1036 erg s−1). We measured temporal quantities, like the rise time to and the decay time from the peak of the flares, their duration and the time interval between adjacent flares. We also estimated the peak luminosity, average accretion rate, and energy release in the flares. The observed soft X-ray properties of low-luminosity flaring activity from SFXTs is in qualitative agreement with what is expected by the application of the Rayleigh–Taylor instability model in accreting plasma near the neutron star magnetosphere. In the case of rapidly rotating neutron stars, sporadic accretion from temporary discs cannot be excluded.
33
Newby, L. M., L. White, S. M. DiBartolomeis, B. J. Walker, H. B. Dowse, J. M. Ringo, N. Khuda, and F. R. Jackson. "Mutational analysis of the Drosophila miniature-dusky (m-dy) locus: effects on cell size and circadian rhythms." Genetics 128, no. 3 (July 1, 1991): 571–82. http://dx.doi.org/10.1093/genetics/128.3.571.
Full textAbstract:
Abstract A mutational analysis has been performed to explore the function of the Drosophila melanogaster miniature-dusky (m-dy) locus. Mutations at this locus affect wing development, fertility and behavior. The genetic characterization of 13 different mutations suggests that m and dy variants are alleles of a single complex gene. All of these mutations alter wing size, apparently by reducing the volume of individual epidermal cells of the developing wing. In m mutants, epidermal cell boundaries persist in the mature wing, whereas they normally degenerate 1-2 hr after eclosion in wild-type or dy flies. This has permitted the direct visualization of cell size differences among several m mutants. Mutations at the m-dy locus also affect behavioral processes. Three out of nine dy alleles (dyn1, dyn3 and dyn4) lengthen the circadian period of the activity and eclosion rhythms by approximately 1.5 hr. In contrast, m mutants have normal circadian periods, but an abnormally large percentage of individuals express aperiodic bouts of activity. These behavior genetic studies also indicate that an existing "rhythm" mutation known as Andante is an allele of the m-dy locus. The differential effects of certain m-dy mutations on wing and behavioral phenotypes suggest that separable domains of function exist within this locus.
34
Hunter, John D., and John G. Milton. "Amplitude and Frequency Dependence of Spike Timing: Implications for Dynamic Regulation." Journal of Neurophysiology 90, no. 1 (July 2003): 387–94. http://dx.doi.org/10.1152/jn.00074.2003.
Full textAbstract:
The spike-time reliability of motoneurons in the Aplysia buccal motor ganglion was studied as a function of the frequency content and the relative amplitude of the fluctuations in the neuronal input, calculated as the coefficient of variation (CV). Measurements of spike-time reliability to sinusoidal and aperiodic inputs, as well as simulations of a noisy leaky integrate-and-fire neuron stimulated by spike trains drawn from a periodically modulated process, demonstrate that there are three qualitatively different CV-dependent mechanisms that determine reliability: noise-dominated (CV < 0.05 for Aplysia motoneurons) where spike timing is unreliable regardless of frequency content; resonance-dominated (CV ≈ 0.05–0.25) where reliability is reduced by removal of input frequencies equal to motoneuron firing rate; and amplitude-dominated (CV >0.35) where reliability depends on input frequencies greater than motoneuron firing rate. In the resonance-dominated regime, changes in the activity of the presynaptic inhibitory interneuron B4/5 alter motoneuron spike-time reliability. The increases or decreases in reliability occur coincident with small changes in motoneuron spiking rate due to changes in interneuron activity. Injection of a hyperpolarizing current into the motoneuron reproduces the interneuron-induced changes in reliability. The rate-dependent changes in reliability can be understood from the phase-locking properties of regularly spiking motoneurons to periodic inputs. Our observations demonstrate that the ability of a neuron to support a spike-time code can be actively controlled by varying the properties of the neuron and its input.
35
Keating, J. G., and W. T. Thach. "No Clock Signal in the Discharge of Neurons in the Deep Cerebellar Nuclei." Journal of Neurophysiology 77, no. 4 (April 1, 1997): 2232–34. http://dx.doi.org/10.1152/jn.1997.77.4.2232.
Full textAbstract:
Keating, J. G. and W. T. Thach. No clock signal in the discharge of neurons in the deep cerebellar nuclei. J. Neurophysiol. 77: 2232–2234, 1997. We examined the spike activity of deep cerebellar nuclear cells recorded from awake, behaving monkeys to determine if there was a tendency for periodic discharge at or near 10 Hz. Data were obtained from four Rhesus monkeys trained to perform either targeted flexions and extensions of the wrist in relation to a visual cue (2 monkeys) or instrumented digit movements and natural reaches (2 monkeys). We determined the interspike intervals of 274 isolated cells. We looked for periodicity by autocorrelating the interval data and Fourier transforming the resulting autocorrelation function. The autocorrelograms and the Fourier transforms failed to reveal periodicity at or near 10 Hz for any cell. This lack of oscillatory discharge in deep nuclear cells of the cerebellum is consistent with our previously reported results that the complex spike of the Purkinje cell is aperiodic. Our failure to observe a clocklike timing signal in awake, behaving animals in either the Purkinje cell complex spike or the deep nuclear cell discharge argues against a popular idea that the inferior olive may act through the cerebellum as a motor clock.
36
Lattenkamp, Ella Z., Meike Linnenschmidt, Eva Mardus, Sonja C. Vernes, Lutz Wiegrebe, and Michael Schutte. "The vocal development of the pale spear-nosed bat is dependent on auditory feedback." Philosophical Transactions of the Royal Society B: Biological Sciences 376, no. 1836 (September 6, 2021): 20200253. http://dx.doi.org/10.1098/rstb.2020.0253.
Full textAbstract:
Human vocal development and speech learning require acoustic feedback, and humans who are born deaf do not acquire a normal adult speech capacity. Most other mammals display a largely innate vocal repertoire. Like humans, bats are thought to be one of the few taxa capable of vocal learning as they can acquire new vocalizations by modifying vocalizations according to auditory experiences. We investigated the effect of acoustic deafening on the vocal development of the pale spear-nosed bat. Three juvenile pale spear-nosed bats were deafened, and their vocal development was studied in comparison with an age-matched, hearing control group. The results show that during development the deafened bats increased their vocal activity, and their vocalizations were substantially altered, being much shorter, higher in pitch, and more aperiodic than the vocalizations of the control animals. The pale spear-nosed bat relies on auditory feedback for vocal development and, in the absence of auditory input, species-atypical vocalizations are acquired. This work serves as a basis for further research using the pale spear-nosed bat as a mammalian model for vocal learning, and contributes to comparative studies on hearing impairment across species. This article is part of the theme issue ‘Vocal learning in animals and humans’.
37
Simard, Corinne, and Paul Charbonneau. "Grand Minima in a spherical non-kinematic α2Ω mean-field dynamo model." Journal of Space Weather and Space Climate 10 (2020): 9. http://dx.doi.org/10.1051/swsc/2020006.
Full textAbstract:
We present a non-kinematic axisymetric α2Ω mean-field dynamo model in which the complete α-tensor and mean differential rotation profile are both extracted from a global magnetohydrodynamical simulation of solar convection producing cycling large-scale magnetic fields. The nonlinear backreaction of the Lorentz force on differential rotation is the only amplitude-limiting mechanism introduced in the mean-field model. We compare and contrast the amplitude modulation patterns characterizing this mean-field dynamo, to those already well-studied in the context of non-kinematic αΩ models using a scalar α-effect. As in the latter, we find that large quasi-periodic modulation of the primary cycle are produced at low magnetic Prandtl number (Pm), with the ratio of modulation period to the primary cycle period scaling inversely with Pm. The variations of differential rotation remain well within the bounds set by observed solar torsional oscillations. In this low-Pm regime, moderately supercritical solutions can also exhibit aperiodic Maunder Minimum-like periods of strongly reduced cycle amplitude. The inter-event waiting time distribution is approximately exponential, in agreement with solar activity reconstructions based on cosmogenic radioisotopes. Secular variations in low-latitude surface differential rotation during Grand Minima, as compared to epochs of normal cyclic behavior, are commensurate in amplitude with historical inferences based on sunspot drawings. Our modeling results suggest that the low levels of observed variations in the solar differential rotation in the course of the activity cycle may nonetheless contribute to, or perhaps even dominate, the regulation of the magnetic cycle amplitude.
38
Paradise, Adiv, Cesar B. Rocha, Pragallva Barpanda, and Noboru Nakamura. "Blocking Statistics in a Varying Climate: Lessons from a “Traffic Jam” Model with Pseudostochastic Forcing." Journal of the Atmospheric Sciences 76, no. 10 (September 12, 2019): 3013–27. http://dx.doi.org/10.1175/jas-d-19-0095.1.
Full textAbstract:
Abstract Recently Nakamura and Huang proposed a semiempirical, one-dimensional model of atmospheric blocking based on the observed budget of local wave activity in the boreal winter. The model dynamics is akin to that of traffic flow, wherein blocking manifests as traffic jams when the streamwise flux of local wave activity reaches capacity. Stationary waves modulate the jet stream’s capacity to transmit transient waves and thereby localize block formation. Since the model is inexpensive to run numerically, it is suited for computing blocking statistics as a function of climate variables from large-ensemble, parameter sweep experiments. We explore sensitivity of blocking statistics to (i) stationary wave amplitude, (ii) background jet speed, and (iii) transient eddy forcing, using frequency, persistence, and prevalence as metrics. For each combination of parameters we perform 240 runs of 180-day simulations with aperiodic transient eddy forcing, each time randomizing the phase relations in forcing. The model climate shifts rapidly from a block-free state to a block-dominant state as the stationary wave amplitude is increased and/or the jet speed is decreased. When eddy forcing is increased, prevalence increases similarly but frequency decreases as blocks merge and become more persistent. It is argued that the present-day climate lies close to the boundary of the two states and hence its blocking statistics are sensitive to climate perturbations. The result underscores the low confidence in GCM-based assessment of the future trend of blocking under a changing climate, while it also provides a theoretical basis for evaluating model biases and understanding trends in reanalysis data.
39
KAY, LESLIE, KOJI SHIMOIDE, and WALTER J. FREEMAN. "COMPARISON OF EEG TIME SERIES FROM RAT OLFACTORY SYSTEM WITH MODEL COMPOSED OF NONLINEAR COUPLED OSCILLATORS." International Journal of Bifurcation and Chaos 05, no. 03 (June 1995): 849–58. http://dx.doi.org/10.1142/s0218127495000636.
Full textAbstract:
The so-called “spontaneous,” background, or “basal” time series of electroencephalographic (EEG) data from rat olfactory cortex are compared with those generated by a model of the ol-factory system, denoted KIII, composed of nonlinear coupled second order ODEs with feedback delay. Each ODE (KO) represents a neural mass having either excitatory or inhibitory output to the ODEs to which it connects. Connected mutually inhibitory or mutually excitatory pairs represent populations of similar neurons interacting to form one structure (KI set). A connected set (KII set) of excitatory and inhibitory KI sets (KIe and KIi) represents the activity of a gross structure in the olfactory system (the olfactory bulb—OB, anterior olfactory nucleus—AON, and prepyriform cortex—PPC or PC). The set of KII sets connected with dispersion-delay feedback pathways (KIII set) form a model of the first central stage of olfactory perceptual processing upon olfactory stimulation, with transition on receptor input from a self-sustained basal state of activity to an induced burst. Both basal and stimulated states are studied using amplitude histograms, power spectra, attractor reconstruction, visual inspection of traces, and correlation. A comparison shows that the two systems are similar, having broad spectra, correlation functions that rapidly go to zero, and gaussian amplitude histograms. Activity is nearly periodic and higher amplitude in the excited state and aperiodic, lower amplitude in the basal state with close to 1/f falloff. Cross spectra between OB and PPC show wide frequency bands of coherent high frequency activity in both the model and rat. The excited state nearly periodic frequencies differ between the KIII model and rat (30–60 Hz in KIII, 50–100 Hz in rat EEG), because the KIII model was developed for the cat and the rabbit, which have lower frequencies than the rat. These benchmarks may be used to evaluate the physiological validity of the output produced by a proposed model, as all components of the system and its connectivity were derived from or evaluated by physiological data.
40
Remsberg, E. E. "Methane as a diagnostic tracer of changes in the Brewer–Dobson circulation of the stratosphere." Atmospheric Chemistry and Physics 15, no. 7 (April 7, 2015): 3739–54. http://dx.doi.org/10.5194/acp-15-3739-2015.
Full textAbstract:
Abstract. This study makes use of time series of methane (CH4) data from the Halogen Occultation Experiment (HALOE) to detect whether there were any statistically significant changes of the Brewer–Dobson circulation (BDC) within the stratosphere during 1992–2005. The HALOE CH4 profiles are in terms of mixing ratio versus pressure altitude and are binned into latitude zones within the Southern Hemisphere and the Northern Hemisphere. Their separate time series are then analyzed using multiple linear regression (MLR) techniques. The CH4 trend terms for the Northern Hemisphere are significant and positive at 10° N from 50 to 7 hPa and larger than the tropospheric CH4 trends of about 3% decade−1 from 20 to 7 hPa. At 60° N the trends are clearly negative from 20 to 7 hPa. Their combined trends indicate an acceleration of the BDC in the middle stratosphere of the Northern Hemisphere during those years, most likely due to changes from the effects of wave activity. No similar significant BDC acceleration is found for the Southern Hemisphere. Trends from HALOE H2O are analyzed for consistency. Their mutual trends with CH4 are anti-correlated qualitatively in the middle and upper stratosphere, where CH4 is chemically oxidized to H2O. Conversely, their mutual trends in the lower stratosphere are dominated by their trends upon entry to the tropical stratosphere. Time series residuals for CH4 in the lower mesosphere also exhibit structures that are anti-correlated in some instances with those of the tracer-like species HCl. Their occasional aperiodic structures indicate the effects of transport following episodic, wintertime wave activity. It is concluded that observed multi-year, zonally averaged distributions of CH4 can be used to diagnose major instances of wave-induced transport in the middle atmosphere and to detect changes in the stratospheric BDC.
41
Li, Wenyuan, Igor V. Ovchinnikov, Honglin Chen, Zhe Wang, Albert Lee, Houchul Lee, Carlos Cepeda, Robert N. Schwartz, Karlheinz Meier, and Kang L. Wang. "A Basic Phase Diagram of Neuronal Dynamics." Neural Computation 30, no. 9 (September 2018): 2418–38. http://dx.doi.org/10.1162/neco_a_01103.
Full textAbstract:
The extreme complexity of the brain has attracted the attention of neuroscientists and other researchers for a long time. More recently, the neuromorphic hardware has matured to provide a new powerful tool to study neuronal dynamics. Here, we study neuronal dynamics using different settings on a neuromorphic chip built with flexible parameters of neuron models. Our unique setting in the network of leaky integrate-and-fire (LIF) neurons is to introduce a weak noise environment. We observed three different types of collective neuronal activities, or phases, separated by sharp boundaries, or phase transitions. From this, we construct a rudimentary phase diagram of neuronal dynamics and demonstrate that a noise-induced chaotic phase (N-phase), which is dominated by neuronal avalanche activity (intermittent aperiodic neuron firing), emerges in the presence of noise and its width grows with the noise intensity. The dynamics can be manipulated in this N-phase. Our results and comparison with clinical data is consistent with the literature and our previous work showing that healthy brain must reside in the N-phase. We argue that the brain phase diagram with further refinement may be used for the diagnosis and treatment of mental disease and also suggest that the dynamics may be manipulated to serve as a means of new information processing (e.g., for optimization). Neuromorphic chips, similar to the one we used but with a variety of neuron models, may be used to further enhance the understanding of human brain function and accelerate the development of neuroscience research.
42
Mrázek, Jan. "Comparative Analysis of Sequence Periodicity among Prokaryotic Genomes Points to Differences in Nucleoid Structure and a Relationship to Gene Expression." Journal of Bacteriology 192, no. 14 (May 21, 2010): 3763–72. http://dx.doi.org/10.1128/jb.00149-10.
Full textAbstract:
ABSTRACT Regular spacing of short runs of A or T nucleotides in DNA sequences with a period close to the helical period of the DNA double helix has been associated with intrinsic DNA bending and nucleosome positioning in eukaryotes. Analogous periodic signals were also observed in prokaryotic genomes. While the exact role of this periodicity in prokaryotes is not known, it has been proposed to facilitate the DNA packaging in the prokaryotic nucleoid and/or to promote negative or positive supercoiling. We developed a methodology for assessments of intragenomic heterogeneity of these periodic patterns and applied it in analysis of 1,025 prokaryotic chromosomes. This technique allows more detailed analysis of sequence periodicity than previous methods where sequence periodicity was assessed in an integral form across the whole chromosome. We found that most genomes have the periodic signal confined to several chromosomal segments while most of the chromosome lacks a strong sequence periodicity. Moreover, there are significant differences among different prokaryotes in both the intensity and persistency of sequence periodicity related to DNA curvature. We proffer that the prokaryotic nucleoid consists of relatively rigid sections stabilized by short intrinsically bent DNA segments and characterized by locally strong periodic patterns alternating with regions featuring a weak periodic signal, which presumably permits higher structural flexibility. This model applies to most bacteria and archaea. In genomes with an exceptionally persistent periodic signal, highly expressed genes tend to concentrate in aperiodic sections, suggesting that structural heterogeneity of the nucleoid is related to local differences in transcriptional activity.
43
Remsberg, E. E. "Methane as a diagnostic tracer of changes in the net circulation of the middle atmosphere." Atmospheric Chemistry and Physics Discussions 14, no. 17 (September 18, 2014): 24183–220. http://dx.doi.org/10.5194/acpd-14-24183-2014.
Full textAbstract:
Abstract. This study makes use of time series of methane (CH4) data from the Halogen Occultation Experiment (HALOE) to determine whether there were any statistically significant changes of the net circulation within the stratosphere and lower mesosphere during 1992–2005. HALOE CH4 profiles in terms of mixing ratio vs. pressure-altitude are binned into subtropical and extratropical latitude zones of the southern and of the Northern Hemisphere, and their separate time series are then analyzed using multiple linear regression (MLR) techniques. A positive trend in the subtropics and a negative trend in the extratropics is interpreted as indicating an acceleration of the net circulation. A significant acceleration is found in the Northern Hemisphere from 20 hPa to 7 hPa, a likely indication of changes from the effects of wave activity during those years. No similar acceleration is found in the Southern Hemisphere. The trends from HALOE H2O are analyzed and compared with those from CH4 for consistency because H2O is a primary product in the upper stratosphere of the chemical conversion of CH4. The CH4 and H2O trends have a ratio of nearly 2 : 1, and they are anti-correlated most clearly near the stratopause in the southern extratropics. Seasonal anomalies are found in the HALOE CH4 time series of the lower mesosphere, and they are ascribed to wave-driven, secondary residual circulation cells associated with the descent of the SAO westerlies. The time series residuals for CH4 of the lower mesosphere also exhibit aperiodic structure, and it is anti-correlated with that of the tracer-like species HCl. Such structure indicates the effects of variations in the wave forcing. It is concluded that multi-year, global-scale distributions of CH4 are very useful for diagnosing large-scale changes of the net transport within the middle atmosphere.
44
Winder, Monika, and James E. Cloern. "The annual cycles of phytoplankton biomass." Philosophical Transactions of the Royal Society B: Biological Sciences 365, no. 1555 (October 12, 2010): 3215–26. http://dx.doi.org/10.1098/rstb.2010.0125.
Full textAbstract:
Terrestrial plants are powerful climate sentinels because their annual cycles of growth, reproduction and senescence are finely tuned to the annual climate cycle having a period of one year. Consistency in the seasonal phasing of terrestrial plant activity provides a relatively low-noise background from which phenological shifts can be detected and attributed to climate change. Here, we ask whether phytoplankton biomass also fluctuates over a consistent annual cycle in lake, estuarine–coastal and ocean ecosystems and whether there is a characteristic phenology of phytoplankton as a consistent phase and amplitude of variability. We compiled 125 time series of phytoplankton biomass (chlorophyll a concentration) from temperate and subtropical zones and used wavelet analysis to extract their dominant periods of variability and the recurrence strength at those periods. Fewer than half (48%) of the series had a dominant 12-month period of variability, commonly expressed as the canonical spring-bloom pattern. About 20 per cent had a dominant six-month period of variability, commonly expressed as the spring and autumn or winter and summer blooms of temperate lakes and oceans. These annual patterns varied in recurrence strength across sites, and did not persist over the full series duration at some sites. About a third of the series had no component of variability at either the six- or 12-month period, reflecting a series of irregular pulses of biomass. These findings show that there is high variability of annual phytoplankton cycles across ecosystems, and that climate-driven annual cycles can be obscured by other drivers of population variability, including human disturbance, aperiodic weather events and strong trophic coupling between phytoplankton and their consumers. Regulation of phytoplankton biomass by multiple processes operating at multiple time scales adds complexity to the challenge of detecting climate-driven trends in aquatic ecosystems where the noise to signal ratio is high.
45
Keating, J. G., and W. T. Thach. "Nonclock behavior of inferior olive neurons: interspike interval of Purkinje cell complex spike discharge in the awake behaving monkey is random." Journal of Neurophysiology 73, no. 4 (April 1, 1995): 1329–40. http://dx.doi.org/10.1152/jn.1995.73.4.1329.
Full textAbstract:
1. Complex spikes of cerebellar Purkinje cells recorded from awake, behaving monkeys were studied to determine the extent to which their discharge could be quantified as periodic. Three Rhesus monkeys were trained to perform up to five different tasks involving rotation of the wrist in relation to a visual cue. Complex spike activity was recorded during task performance and intertrial time. Interspike intervals were determined from the discharge of each of 89 Purkinje cells located throughout lobules IV, V, and VI. Autocorrelation and Fourier transform of the autocorrelation function were performed on the data. In addition, the activity from one cell was transformed so that the discharge occurred on the beat of a 10-Hz clock, and in a further transformation, on the beat of a noisy 10-Hz clock. These transformed data were then analyzed as described above. 2. Fourier transform of the autocorrelogram function of the data that had been transformed to a 10-Hz clock, and that of the noisy 10-Hz clock, both showed a prominent peak at 10 Hz. However, the autocorrelograms and the Fourier transforms of the autocorrelogram functions failed to reveal a prominent periodicity for the actual discharge of any of cells, at any frequency up to 100 Hz: the discharge appeared random with respect to the interspike interval. The discharge was not random with respect to behavior. Complex spike activity was commonly time locked to the start of wrist movement. We examined this discharge to see whether oscillatory discharge could be seen after alignment of the data on the start of wrist movement, or after alignment of the data on the complex spike occurring peri-start of wrist movement. No oscillation was seen for either alignment. 3. The inferior olive, which sends its climbing fibers to the cerebellum, has been implicated in such different activities as 1) pathological tremor of the soft palate, 2) physiological tremor, 3) the normal initiation of all bodily movement, and 4) motor learning. Previous work in pharmacologically or surgically treated animals has shown that, under some conditions, the discharge of these neurons is periodic and synchronous. This firing pattern has been interpreted to support a role in the first two activities. But measurements reported here in the awake monkey show just the opposite: the discharge is aperiodic to the extent of being random. As such, the inferior olive cannot be a "motor clock" in the general role that has been proposed.(ABSTRACT TRUNCATED AT 400 WORDS)
46
Teixeira, G. D. C., M. S. N. Kumar, L. Smith, P. W. Lucas, C. Morris, J. Borissova, M. J. P. F. G. Monteiro, et al. "Photometric variability of massive young stellar objects." Astronomy & Astrophysics 619 (November 2018): A41. http://dx.doi.org/10.1051/0004-6361/201833667.
Full textAbstract:
The Vista Variables in the Via Lactea (VVV) survey has allowed for an unprecedented number of multi-epoch observations of the southern Galactic plane. In a recent paper, 13 massive young stellar objects (MYSOs) have already been identified within the highly variable (ΔKs > 1 mag) YSO sample of another published work. This study aims to understand the general nature of variability in MYSOs. Here we present the first systematic study of variability in a large sample of candidate MYSOs. We examined the data for variability of the putative driving sources of all known Spitzer extended green objects (EGOs; 270) and bright 24 μm sources coinciding with the peak of 870 μm detected ATLASGAL clumps (448), a total of 718 targets. Of these, 190 point sources (139 EGOs and 51 non-EGOs) displayed variability (IQR > 0.05, ΔKs > 0.15 mag). 111 and 79 light-curves were classified as periodic and aperiodic respectively. Light-curves have been sub-classified into eruptive, dipper, fader, short-term-variable and long-period-variable-YSO categories. Lomb-Scargle periodogram analysis of periodic light-curves was carried out. 1–870 μm spectral energy distributions of all the variable sources were fitted with YSO models to obtain the representative properties of the variable sources. 41% of the variable sources are represented by > 4 M⊙ objects, and only 6% were modelled as > 8 M⊙ objects. The highest-mass objects are mostly non-EGOs, and deeply embedded, as indicated by nearly twice the extinction when compared with EGO sources. By placing them on the HR diagram we show that most of the lower mass, EGO type objects are concentrated on the putative birth-line position, while the luminous non-EGO type objects group around the zero-age-main-sequence track. Some of the most luminous far infrared (FIR) sources in the massive clumps and infrared quiet driving sources of EGOs have been missed out by this study owing to an uniform sample selection method. A high rate of detectable variability in EGO targets (139 out of 153 searched) implies that near-infrared variability in MYSOs is closely linked to the accretion phenomenon and outflow activity.
47
Chernogor, L. F., and Y. B. Milovanov. "Ionospheric effects of the August 11, 2018, solar eclipse over the People’s Republic of China." Kinematika i fizika nebesnyh tel (Online) 36, no. 6 (November 1, 2020): 37–64. http://dx.doi.org/10.15407/kfnt2020.06.037.
Full textAbstract:
The purpose of the work is to describe the ionospheric effects of the August 11, 2018 partial solar eclipse (SE) that occurred over the People’s Republic of China, as observed via GPS technology. SEs present rare phenomena of nature. In the course of 2 to 3 hours, the rearrangement of processes acting at the Earth’s surface, in the atmosphere, geospace, i.e., in the Earth — atmosphere — ionosphere — magnetosphere system (EAIMS), occurs. The response of this system depends on the solar activity, season, time of day, and on the state of atmospheric and space weather. Therefore, the study of the EAIMS response to SEs remains an urgent need. The response is accompanied by controllable dynamic processes, the study of which improves our understanding of the near-Earth environment. The study of the EAIMS response to SEs is of fundamental importance to science. Its practical applications include the following. The SE give rise to significant perturbations in the EAIMS, which affect the propagation of radio waves virtually in all frequency bands, and consequently deteriorate the operation of radar, radio astronomy, and radio navigation systems, as well as the instruments for remotely sensing the medium. The SE effects have been studied for over more than about 100 years. Thus far, the following regular effects have been quite well studied: decreases in the electron density, electron and ion temperatures, variations in ion composition, and plasma vertical movements. The irregular effects have been studied to a significantly smaller degree, and they can vary from one solar eclipse to another. The main feature of the SE over the PRC was the fact that it was observed during before local time sunset period. The maximum phase of the eclipse within the PRC area varied from 0.07 to 0.52, while the Sun’s surface area occulted by the moon was observed to be 0.02—0.42. The beginning of the eclipse over the PRC was observed to occur in the 09:54—10:05 UT period, and the end varied from 10:07 UT to 11:10 UT. The SE duration varied from a few minutes to approximately 67 min. The insignificant duration of the eclipse and the dusk terminator affected the SE effects. The state of space weather during the solar eclipse was conducive to observing the SE effects occurring in the ionosphere. To reveal the ionospheric response to the August 11, 2018, SE, the global navigation satellite system data were processed. The ionospheric time delay and, respectively, the vertical total electron content (TEC), were calculated combining the pseudo range and integrated phase data at two frequencies. Regardless of the dusk terminator influence, we have managed to confidently detect the ionospheric SE effects, which proved to be sufficiently small because of small values of the SE phase. Over the People’s Republic of China area, a funnel-shaped decrease in TEC was observed to occur approximately 1,300 km in latitude and 2,000 km in longitude. The TEC decrease was observed to be 7 %. The solar eclipse was accompanied by the generation of aperiodic TEC disturbances at a rate of 0.4—0.8 TEC unit/h and 105-min in duration. Wave disturbances caused by the SE were not observed confidently, which is due to the small value of the SE phase and insignificant disturbances in the electron density.
48
Al Saadi, Dr Maysoun Taha Mahmoud. "Thermal characteristics and their impact on tourism in Iraq." ALUSTATH JOURNAL FOR HUMAN AND SOCIAL SCIENCES 223, no. 2 (October 28, 2018): 13–32. http://dx.doi.org/10.36473/ujhss.v223i2.335.
Full textAbstract:
Tourism is know as asset activities protied by in dividuals, travelers and resident in places out side the usual environment for aperiod not exceeding one year for resection, trade or other purpose. Classified Tourism to several patter including religious, recreational and the rapeution sports, etc. and Tourism is of great sign if icance in advancing economic and social environment forwards asit has become the activity of the fast growing markets and depend on the climate in the first place and the study relied style of analysis climate Date for dry temperature the feeling of perfect comfort classified province un comfortable cold winter an noving to the city of mousl, Rutba, Baghdad and given the symbol Dandis given the cities of Amara and Kut code c from the comfort of the third place, While the city of Basra are given the symbol A perfect comfort. And the southen areas attractive for Tourism in he winter especially the city of Basra is considerd The Northern regions, repellent for Tourism especially the city of mousl. Deduce the values of rates of comfort effective temperature by feeling annoying un comfort extreme heat in all of the month of June, July Augustin September in all the governora tes of Iraq. Especially in the Southeren provin while Rutba city is best cities in Iraq in terms of feeling comfort for years The ideal comfort confined values (15-20) to guide, the effective temperature (17- 25) and Applied the equation on the Iraqi Provineces of mosul, Baghdad, Rutba, Kut, Amarah, Basea for the period from 2000- 2010 and davis also used the modified equation that uses dry temperature and the number of hours of sun shine and relative humidity which give the tourist guide climate and applied for stations distributed across Iraq.
49
van Heumen, Saskia, Jeremy T. Moreau, Elisabeth Simard-Tremblay, Steffen Albrecht, Roy WR Dudley, and Sylvain Baillet. "Case Report: Aperiodic Fluctuations of Neural Activity in the Ictal MEG of a Child With Drug-Resistant Fronto-Temporal Epilepsy." Frontiers in Human Neuroscience 15 (March 4, 2021). http://dx.doi.org/10.3389/fnhum.2021.646426.
Full textAbstract:
Successful surgical treatment of patients with focal drug-resistant epilepsy remains challenging, especially in cases for which it is difficult to define the area of cortex from which seizures originate, the seizure onset zone (SOZ). Various diagnostic methods are needed to select surgical candidates and determine the extent of resection. Interictal magnetoencephalography (MEG) with source imaging has proven to be useful for presurgical evaluation, but the use of ictal MEG data remains limited. The purpose of the present study was to determine whether pre-ictal variations of spectral properties of neural activity from ictal MEG recordings are predictive of SOZ location.We performed a 4 h overnight MEG recording in an 8-year-old child with drug-resistant focal epilepsy of suspected right fronto-temporal origin and captured one ~45-s seizure. The patient underwent a right temporal resection from the anterior temporal neocortex and amygdala to the mid-posterior temporal neocortex, sparing the hippocampus proper. She remains seizure-free 21 months postoperatively. The histopathological assessment confirmed frank focal cortical dysplasia (FCD) type IIa in the MEG-defined SOZ, which was based on source imaging of averaged ictal spikes at seizure onset. We investigated temporal changes (inter-ictal, pre-ictal, and ictal periods) together with spatial differences (SOZ vs. control regions) in spectral parameters of background brain activity, namely the aperiodic broadband offset and slope, and assessed how they confounded the interpretation of apparent variations of signal power in typical electrophysiological bands. Our data show that the SOZ was associated with a higher aperiodic offset and exponent during the seizure compared to control regions. Both parameters increased in all regions from 2 min before the seizure onwards. Regions anatomically closer to the SOZ also expressed higher values compared to contralateral regions, potentially indicating ictal spread. We also show that narrow-band power changes were caused by these fluctuations in the aperiodic component of ongoing brain activity. Our results indicate that the broadband aperiodic component of ongoing brain activity cannot be reduced to background noise of no physiological interest, and rather may be indicative of the neuropathophysiology of the SOZ. We believe these findings will inspire future studies of ictal MEG cases and confirm their significance.
50
Manohara, H. T., and B. P. Harish. "A Novel Feasibility Test for Energy Minimization of Real-Time Mixed Task Sets for DVS-Enabled Uniprocessor System." Journal of Circuits, Systems and Computers, September 23, 2021, 2250052. http://dx.doi.org/10.1142/s0218126622500529.
Full textAbstract:
With advancements in computing and communication technologies on mobile devices, the performance requirements of embedded processors have significantly increased, resulting in a corresponding increase in its energy consumption. Dynamic scaling of operating voltage and operating frequency has a strong correlation to energy minimization in CMOS real-time circuits. Simultaneous optimization of ([Formula: see text], [Formula: see text] pairs under dynamic activity levels is thus extensively investigated over several years. The supply voltage is tuned dynamically during runtime (DVS), with a fixed threshold voltage, to achieve energy minimization. This work addresses the issue of maximizing the energy efficiency of real-time periodic, aperiodic and mixed task sets, in a uniprocessor system, by developing a novel task feasibility methodology, with a novel processor performance-based constraint, to generate the optimal operating supply voltage to the individual task of task sets. The energy minimization of real-time mixed task sets is formulated as Geometric Programming (GP) problem, by varying frequency for periodic tasks sets and keeping fixed frequency for aperiodic tasks set, over a range of task sets and hence computing optimal operating voltages. Simulation experiments show energy savings on the cumulative basis of 50%, 38% and 29% for periodic, aperiodic and mixed task sets, respectively, based on the processing timing constraints of task sets.