Fast Bursts Research Articles

Mechanisms leading to bursting oscillations in the system of predator–prey communities coupled by migrations

The purpose is to study the periodic regimes of the dynamics for two non-identical predator– prey communities coupled by migrations, associated with the partial synchronization of fluctuations in the abundance of communities. The combination of fluctuations in neighboring sites leads to the regimes that include both fast bursts (bursting oscillations) and slow oscillations (tonic spiking). These types of activity are characterized by a different ratio of synchronous and non-synchronous dynamics of communities in certain periods of time. In this paper, we describe scenarios of the transition between different types of burst activity. These types of dynamics differ from each other not so much in size, shape, and number of spikes in a burst, but in the order of these bursts relative to the slow-fast cycle. Methods. To study the proposed model, we use the bifurcation analysis methods of dynamic systems, as well as geometric methods based on the division of the full system into fast and slow equations (subsystems). Results. We showed that the dynamics of the first subsystem with a slow-fast limit cycle directly determines the dynamics of the second one with burst activity through a smooth dependence of regime on the number of predators and a non-smooth dependence on the number of prey. We constructed the invariant manifolds on which there are parts of dynamics with tonic (slow manifold) and burst (fast manifold) activity of the full system. Conclusion. We described the scenario for bursting with different waveforms, which are determined by the appearance of the fast invariant manifold and the location of its parts relative to the slow-fast cycle. The transitions between different types of burst are accompanied by a change in the oscillation period, the degree of synchronization, and, as a result, the dynamics becomes quasi-periodic when both communities are not synchronous with each other.

Integrated Circuit Robustness Improvement Analysis, Modeling and Measurement Against Fast Transient Burst Events

Integrated Circuit Robustness Improvement Analysis, Modeling and Measurement Against Fast Transient Burst Events

Machine learning provides insight into models of heterogeneous electrical activity in human beta-cells

Understanding how heterogeneous cellular responses emerge from cell-to-cell variations in expression and function of subcellular components is of general interest. Here, we focus on human insulin-secreting beta-cells, which are believed to constitute a population in which heterogeneity is of physiological importance. We exploit recent single-cell electrophysiological data that allow biologically realistic population modeling of human beta-cells that accounts for cellular heterogeneity and correlation between ion channel parameters. To investigate how ion channels influence the dynamics of our updated mathematical model of human pancreatic beta-cells, we explore several machine learning techniques to determine which model parameters are important for determining the qualitative patterns of electrical activity of the model cells. As expected, K＋ channels promote absence of activity, but once a cell is active, they increase the likelihood of having action potential firing. HERG channels were of great importance for determining cell behavior in most of the investigated scenarios. Fast bursting is influenced by the time scales of ion channel activation and, interestingly, by the type of Ca2＋ channels coupled to BK channels in BK-CaV complexes. Slow, metabolically driven oscillations are promoted mostly by K(ATP) channels. In summary, combining population modeling with machine learning analysis provides insight into the model and generates new hypotheses to be investigated both experimentally, via simulations and through mathematical analysis.

Synchronous firing of dorsal horn neurons at the origin of dorsal root reflexes in naïve and paw-inflamed mice.

Spinal interneurons located in the dorsal horn induce primary afferent depolarization (PAD) controlling the excitability of the afferent’s terminals. Following inflammation, PAD may reach firing threshold contributing to maintain inflammation and pain. Our aim was to study the collective behavior of dorsal horn neurons, its relation to backfiring of primary afferents and the effects of a peripheral inflammation in this system. Experiments were performed on slices of spinal cord obtained from naïve adult mice or mice that had suffered an inflammatory pretreatment. Simultaneous recordings from groups of dorsal horn neurons and primary afferents were obtained and machine-learning methodology was used to analyze effective connectivity between them. Dorsal horn recordings showed grouping of spontaneous action potentials from different neurons in “population bursts.” These occurred at irregular intervals and were formed by action potentials from all classes of neurons recorded. Compared to naïve, population bursts from treated animals concentrated more action potentials, had a faster onset and a slower decay. Population bursts were disrupted by perfusion of picrotoxin and held a strong temporal correlation with backfiring of afferents. Effective connectivity analysis allowed pinpointing specific neurons holding pre- or post-synaptic relation to the afferents. Many of these neurons had an irregular fast bursting pattern of spontaneous firing. We conclude that population bursts contain action potentials from neurons presynaptic to the afferents which are likely to control their excitability. Peripheral inflammation may enhance synchrony in these neurons, increasing the chance of triggering action potentials in primary afferents and contributing toward central sensitization.

Multiple conjugate observations of magnetospheric fast flow bursts using THEMIS observations

Abstract. Magnetotail earthward fast flow bursts can transport most magnetic flux and energy into the inner magnetosphere. These fast flow bursts are generally an order of magnitude higher than the typical convection speeds that are azimuthally localised (1–3 RE) and are flanked by plasma vortices, which map to ionospheric plasma vortices of the same sense of rotation. This study uses a multipoint analysis of conjugate magnetospheric and ionospheric observations to investigate the magnetospheric and ionospheric responses to fast flow bursts that are associated with both substorms and pseudobreakups. We study in detail what properties control the differences in the magnetosphere–ionosphere responses between substorm fast flow bursts and pseudobreakup events, and how these differences lead to different ionospheric responses. The fast flow bursts and pseudobreakup events were observed by the Time History of Events and Macroscale Interaction during Substorms (THEMIS), while the primary ionospheric observations were made by all-sky cameras and magnetometer-based equivalent ionospheric currents. These events were selected when the satellites were at least 6 RE from the Earth in radial distance and a magnetic local time (MLT) region of ± 5 h from local midnight. The results show that the magnetosphere and ionosphere responses to substorm fast flow bursts are much stronger and more structured compared to pseudobreakups, which are more likely to be localised, transient and weak in the magnetosphere. The magnetic flux in the tail is much stronger for strong substorms and much weaker for pseudobreakup events. The Blobe decreases significantly for substorm fast flow bursts compared to pseudobreakup events. The curvature force density for pseudobreakups are much smaller than substorm fast flow events, indicating that the pseudobreakups may not be able to penetrate deep into the inner magnetosphere. This association can help us study the properties and activity of the magnetospheric earthward flow vortices from ground data.

Effects from dayside magnetosphere to distant tail unleashed by a bifurcated, non-reconnecting interplanetary current sheet

Global magnetospheric effects resulting from the passage at Earth of large-scale structures have been well studied. The effects of common and short-term features, such as discontinuities and current sheets (CSs), have not been studied in the same depth. Herein we show how a seemingly unremarkable interplanetary feature can cause widespread effects in the magnetosheath-magnetosphere system. The feature was observed by Advanced Composition Explorer inside an interplanetary coronal mass ejection on 10 January 2004. It contained 1) a magnetic field dip bounded by directional discontinuities in field and flows, occurring together with 2) a density peak in what we identify as a bifurcated, non-reconnecting current sheet. Data from an array of spacecraft in key regions of the magnetosheath/magnetosphere (Geotail, Cluster, Polar, and Defense Meteorological Satellite Program) provide context for Wind’s observations of flapping of the distant (R ∼ −226 RE) magnetotail. In particular, just before the flapping began, Wind observed a hot and tenuous plasma in a magnetic field structure with enhanced field strength, with the By and Bz components rotating in a fast tailward flow burst. Closer inspection reveals a large flux rope (plasmoid) containing lobe plasma in a tail strongly deflected and twisted by interplanetary non-radial flows and magnetic field By. We try to identify the origin of this ‘precursor to flapping’ by looking at data from the various spacecraft. Working back towards the dayside, we discover a chain of effects which we argue were set in motion by the interplanetary CS and its interaction with the bow shock. These effects include 1) a compression and dilation of the magnetosphere, 2) a local deformation of the postnoon magnetopause, and, 3) at the poleward edge of the oval in an otherwise quiet polar cap flow, a strong (3 km/s) sunward flow burst in a double vortex-like structure flanked by two sets of field-aligned currents. Clearly, an intertwined set of phenomena was occurring at the same time. We learn that multi-spacecraft analysis can give us great insight into the magnetospheric response to transient changes in the solar wind.

Electrical explosion in confined space: From warm dense matter to fragmentation

The physical image of the confined electrical explosion in the source region is depicted. Metallic plasma/vapor dynamics and its fragmentation effect (on a confining structure) under μs-timescale are diagnosed via high-speed photography, electrophysical, and spectral measurements. When adding a 1-mm-thick Teflon tube outside the exploding wire, the growth of spatial heterogeneity via electro-thermal instability is largely compressed, and the deposited energy almost doubled from about 85 to 150 J. During the short period after breakdown, considerable energy depositing into the confined space, e.g., 100 J for 0.1 cm3, drives the fast inflation and burst of the 0.5 g confining tube to ∼500 m/s (kinetic energy of ∼62.5 J). Intense plasma jet eruption with a supersonic speed >1.5 km/s and induced shock waves of 2–3 km/s are observed from cracks of the inflated tube. In addition, the erupted plasma jets gradually evolve Rayleigh–Taylor instability and finally cause turbulent mixing with the ambient medium. This mechanism is very likely to explain the plasma cavity evolution in underwater explosion. Interestingly, although the confining effect of water is stronger than a Teflon tube, the latter has a better response to the high-rate impulse loading and absorbs more deposited energy by deformation, phase transition, and acceleration.

Coupling of in vitro Neocortical-Hippocampal Coculture Bursts Induces Different Spike Rhythms in Individual Networks.

Brain-state alternation is important for long-term memory formation. Each brain state can be identified with a specific process in memory formation, e.g., encoding during wakefulness or consolidation during sleeping. The hippocampal-neocortical dialogue was proposed as a hypothetical framework for systems consolidation, which features different cross-frequency couplings between the hippocampus and distributed neocortical regions in different brain states. Despite evidence supporting this hypothesis, little has been reported about how information is processed with shifts in brain states. To address this gap, we developed an in vitro neocortical-hippocampal coculture model to study how activity coupling can affect connections between coupled networks. Neocortical and hippocampal neurons were cultured in two different compartments connected by a micro-tunnel structure. The network activity of the coculture model was recorded by microelectrode arrays underlying the substrate. Rhythmic bursting was observed in the spontaneous activity and electrical evoked responses. Rhythmic bursting activity in one compartment could couple to that in the other via axons passing through the micro-tunnels. Two types of coupling patterns were observed: slow-burst coupling (neocortex at 0.1–0.5 Hz and hippocampus at 1 Hz) and fast burst coupling (neocortex at 20–40 Hz and hippocampus at 4–10 Hz). The network activity showed greater synchronicity in the slow-burst coupling, as indicated by changes in the burstiness index. Network synchronicity analysis suggests the presence of different information processing states under different burst activity coupling patterns. Our results suggest that the hippocampal-neocortical coculture model possesses multiple modes of burst activity coupling between the cortical and hippocampal parts. With the addition of external stimulation, the neocortical-hippocampal network model we developed can elucidate the influence of state shifts on information processing.

AT2020hur: A Possible Optical Counterpart of FRB 180916B

The physical origin of fast radio bursts (FRBs) remains unclear. Finding multiwavelength counterparts of FRBs can provide a breakthrough for understanding their nature. In this work, we perform a systematic search for astronomical transients whose positions are consistent with FRBs. We find an unclassified optical transient AT2020hur (α = 01h58m00.ˢ750 ± 1″, ) that is spatially coincident with the repeating FRB 180916B (α = 01h58m00.ˢ7502 ± 2.3 mas, mas; Marcote et al. 2020). The chance possibility of the AT2020hur–FRB 180916B association is about 0.04%, which corresponds to a significance of 3.5σ. We develop a giant flare (GF) afterglow model to fit AT2020hur. Although the GF afterglow model can interpret the observations of AT2020hur, the derived kinetic energy of such a GF is at least three orders of magnitude larger than that of a typical GF, and a lot of fine-tuning and coincidences are required for this model. Another possible explanation is that AT2020hur might consist of two or more optical flares originating from the FRB source, e.g., fast optical bursts produced by the inverse Compton scattering of FRB emission. Besides, AT2020hur is located in one of the activity windows of FRB 180916B, which provides independent support for the association. This coincidence may be due to the optical counterparts being subject to the same periodic modulation as FRB 180916B, as implied by the prompt FRB counterparts. Future simultaneous observations of FRBs and their optical counterparts may help to reveal their physical origin.

Bursting TENS increases walking endurance more than continuous TENS in middle-aged adults

The application of transcutaneous electrical nerve stimulation (TENS) can improve motor performance in both healthy individuals and those who present with clinically detectable sensory impairments. The purpose of our study was to compare the influence of continuous and intermittent TENS applied to the anterior thigh and tibialis anterior muscles on walking endurance and kinematics in healthy, middle-aged adults. Twenty-seven participants completed 4 trials of the 6-min walk test: Baseline, Continuous TENS (0.2 ms pulses at 50 Hz), Fast burst TENS (seven 0.15 ms pulses in 5 Hz bursts), and Slow burst TENS (seven 0.15 ms pulses in 0.5 Hz bursts). Linear mixed-effects models revealed that participants walked further (p ≤ 0.046) during all three TENS trials compared with Baseline (560 ± 76 m) and that they walked even further during both burst TENS trials (576 ± 83 m and 576 ± 83 m) compared with Continuous TENS (566 ± 79 m). Increases in walking speed were predicted by increases in stride length (p < 0.001) and stride frequency (p < 0.001) with toe-off angle being the only significant predictor (p ≤ 0.013) of both kinematic variables for the increase in walking speed. Bursting TENS was more effective than Continuous TENS at improving walking endurance in middle-aged, healthy adults.

A lexical approach for identifying behavioural action sequences.

Animals display characteristic behavioural patterns when performing a task, such as the spiraling of a soaring bird or the surge-and-cast of a male moth searching for a female. Identifying such recurring sequences occurring rarely in noisy behavioural data is key to understanding the behavioural response to a distributed stimulus in unrestrained animals. Existing models seek to describe the dynamics of behaviour or segment individual locomotor episodes rather than to identify the rare and transient sequences of locomotor episodes that make up the behavioural response. To fill this gap, we develop a lexical, hierarchical model of behaviour. We designed an unsupervised algorithm called "BASS" to efficiently identify and segment recurring behavioural action sequences transiently occurring in long behavioural recordings. When applied to navigating larval zebrafish, BASS extracts a dictionary of remarkably long, non-Markovian sequences consisting of repeats and mixtures of slow forward and turn bouts. Applied to a novel chemotaxis assay, BASS uncovers chemotactic strategies deployed by zebrafish to avoid aversive cues consisting of sequences of fast large-angle turns and burst swims. In a simulated dataset of soaring gliders climbing thermals, BASS finds the spiraling patterns characteristic of soaring behaviour. In both cases, BASS succeeds in identifying rare action sequences in the behaviour deployed by freely moving animals. BASS can be easily incorporated into the pipelines of existing behavioural analyses across diverse species, and even more broadly used as a generic algorithm for pattern recognition in low-dimensional sequential data.

Fast gravitational wave bursts from axion clumps

The axion objects such as axion miniclusters and axion clouds around spinning black holes induce parametric resonances of electromagnetic waves through the axion-photon interaction. In particular, it has been known that the resonances from the axion with the mass around ${10}^{\ensuremath{-}6}\text{ }\text{ }\mathrm{eV}$ may explain the observed fast radio bursts (FRBs). Here we argue that similar bursts of high frequency gravitational waves, which we call fast gravitational wave bursts (FGBs), are generated from axion clumps with the presence of gravitational Chern-Simons (CS) coupling. The typical frequency is half of the axion mass, which in general can range from kHz to GHz. We also discuss the secondary gravitational wave production associated with FRB, as well as the possible host objects of the axion clouds, such as primordial black holes with typical masses around ${10}^{\ensuremath{-}5}\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$. Future detections of FGBs together with the observed FRBs are expected to provide more evidence for the axion.

Constraints on Optical Emission of FAST-detected FRB 20181130B with GWAC Synchronized Observations

Abstract Multiwavelength simultaneous observations are essential to the constraints on the origin of fast radio bursts (FRBs). However, it is a significant observational challenge due to the nature of FRBs as transients with a radio millisecond duration, which occur randomly in the sky regardless of time and position. Here, we report the search for short-time fast optical bursts in the Ground-based Wide Angle Camera (GWAC) archived data associated with FRB 20181130B, which were detected by the Five-hundred-meter Aperture Spherical radio Telescope and recently reported. No new credible sources were detected in all single GWAC images with an exposure time of 10 s, including images with coverage of the expected arrival time in optical wavelength by taking the high dispersion measurements into account. Our results provide a limiting magnitude of 15.43 ± 0.04 mag in the R band, corresponding to a flux density of 1.66 Jy or 8.35 mag in AB system by assuming that the duration of the optical band is similar to that of the radio band of about 10 ms. This limiting magnitude makes the spectral index of α &lt; 0.367 from optical to radio wavelength. The possible existence of longer-duration optical emission was also investigated with upper limits of 0.33 Jy (10.10 mag), 1.74 mJy (15.80 mag), and 0.16 mJy (18.39 mag) for the durations of 50 ms, 10 s, and 6060 s, respectively. This undetected scenario could be partially attributed to the shallow detection capability, as well as the high inferred distance of FRB 20181130B and the low fluence in radio wavelength. The future detectability of optical flashes associated with nearby and bright FRBs are also discussed in this paper.

A New Era of Nuclear Criticality Experiments: The First 10 Years of Godiva IV Operations at NCERC

The work presented in this paper focuses on the first 10 years (2011–2020) of Godiva IV operations at the National Criticality Experiments Research Center (NCERC). Godiva IV is a fast burst critical assembly constructed of approximately 65 kg of highly enriched uranium fuel alloyed with 1.5% molybdenum for strength. Godiva is one of the last such critical assemblies in the United States and can be used for studies of super-prompt-critical behavior as well as irradiations and demonstrations. An overview of the startup of Godiva IV at NCERC is given followed by a summary of the experiments performed utilizing Godiva IV over the first 10 years of operation at NCERC.

Effects of Bubble Injections on the Plasma Sheet Configuration

AbstractThe bimodal transport in the plasma sheet consists of sunward large‐scale, coherent, and slow motion of charged particles in the closed‐field‐line region as well as meso‐scale, localized, and transient fast flow bursts. It has been found that these earthward moving bursty bulk flows, also called “bubbles,” play a crucial role not only in the transporting mass and energy, but also in resolving the pressure‐balance crisis with their integrated effects. In this study, we examine how bubbles can affect the average configuration of the middle and inner plasma sheet using the Inertialized Rice Convection Model (RCM‐I). Bubbles are sporadically imposed at on the nightside plasma sheet, with optimized parameters that constrain their statistical properties. The consequence of the injection of these series of bubbles is evaluated by comparing against observed statistical results, including plasma moments and magnetic field configuration. Our findings confirm that bursty bulk flows are indispensable elements in the magnetotail plasma sheet.

The Chlorate-Nitrous Acid-Iodine-Iodide Oscillating Reaction.

This work presents a new oscillating reaction based on chlorate and observed in a CSTR at room temperature. This can be the first member of a new family of oscillating reactions. In addition, it is also the first oscillating reaction to use nitrous acid as a reactant. Four different behaviors were observed: simple oscillations, mixed mode oscillations, bursts, and quasiperiodicity. The period of oscillations is very short, which is around 1 s. Together with the fact that it also shows fast bursts, it opens the possibility that it can be used to simulate fast biological events, like the neuron’s communications signals.

Uncertainty Evaluation of the Electrical Transient Rise Time

This paper deals with the uncertainty evaluation of the rise time of one pulse of an electrical fast transient burst (EFT/B), as carried out by the National Institute of Metrology, Quality and Technology (Inmetro) of Brazil. The uncertainty sources considered in this evaluation were: the oscilloscope resolution and calibration of voltage and time scale, in the Y-and X-axes, respectively; the bandwidth of the measurement system; the oscilloscope sampling rate; and the repeatability of ten different measurements. Two sets of measurements were taken from two different oscilloscope settings: in the first one, the interpolation function was enabled, and in the other one was disabled. In both cases two components stood out for their huge relative contribution: time reading and repeatability. Considered together, these two components added up approximately 87% of the expanded uncertainty for interpolated samples, and 95% for non-interpolated samples. Also, the results indicate that the oscilloscope interpolation function, if available, must be used, as the expanded uncertainty decreases by 27%. A discussion of the uncertainty budget example in Annex C of the IEC 61000-4-4 standard is presented, concluding that, once the oscilloscope interpolation function is enabled, the other uncertainty components should be considered. The combined relative contribution of these components is larger than the relative contribution of repeatability.

Determination of 232Th in an electrodeposited target by neutron-activation analysis

ABSTRACT An electrodeposited thorium target and a ThO2 sample were irradiated together with fast neutrons using the Chinese Fast Burst Reactor II. The activities of 233Pa in both samples were measured and compared to determine the mass of 232Th deposited on the target. Experimental results showed that the mass of deposited 232Th was 19.6 μg, and the uncertainty was estimated to be 1.4%.

A Nano-Power 0.5 V Event-Driven Digital-LDO with Fast Start-Up Burst Oscillator for SoC-IoT

Towards the integration of Digital-LDO regulators in the ultra-low-power System-On-Chip Internet-of-Things architecture, the D-LDO architecture should constitute the main regulator for powering digital and mixed-signal loads including the SoC system clock. Such an implementation requires an in-regulator clock generation unit that provides an autonomous D-LDO design. In contrast to contemporary D-LDO designs that employ ring-oscillator architecture which start-up time is dependent on the oscillating frequency, this work presents a design with nano-power consumption, fabricated with an active area of 0.035 mm2 at a 55-nm Global Foundries CMOS process that introduces a fast start-up burst oscillator based on a high-gain stage with wake-up time independent of D-LDO frequency. In combination with linear search coarse regulation and asynchronous fine regulation, it succeeds 558 nA minimum quiescent current with CL 75 pF, maximum current efficiency of 99.2% and 1.16x power efficiency improvement compared to analog counterpart oriented to SoC-IoT loads.

Observations and Modeling of the Onset of Fast Reconnection in the Solar Transition Region

Abstract Magnetic reconnection is a fundamental plasma process that plays a critical role not only in energy release in the solar atmosphere, but also in fusion, astrophysics, and other space plasma environments. One of the challenges in explaining solar observations in which reconnection is thought to play a critical role is to account for the transition of the dynamics from a slow quasi-continuous phase to a fast and impulsive energetic burst of much shorter duration. Despite the theoretical progress in identifying mechanisms that might lead to rapid onset, a lack of observations of this transition has left models poorly constrained. High-resolution spectroscopic observations from NASA's Interface Region Imaging Spectrograph now reveal tell-tale signatures of the abrupt transition of reconnection from a slow phase to a fast, impulsive phase during UV bursts or explosive events in the Sun's atmosphere. Our observations are consistent with numerical simulations of the plasmoid instability, and provide evidence for the onset of fast reconnection mediated by plasmoids and new opportunities for remote-sensing diagnostics of reconnection mechanisms on the Sun.