Slow Component Research Articles

Direct observations of a complex coronal web driving highly structured slow solar wind

The solar wind consists of continuous streams of charged particles that escape into the heliosphere from the Sun, and is split into fast and slow components, with the fast wind emerging from the interiors of coronal holes. Near the ecliptic plane, the fast wind from low-latitude coronal holes is interspersed with a highly structured slow solar wind, the source regions and drivers of which are poorly understood. Here we report extreme-ultraviolet observations that reveal a spatially complex web of magnetized plasma structures that persistently interact and reconnect in the middle corona. Coronagraphic white-light images show concurrent emergence of slow wind streams over these coronal web structures. With advanced global magnetohydrodynamics coronal models, we demonstrate that the observed coronal web is a direct imprint of the magnetic separatrix web (S-web). By revealing a highly dynamic portion of the S-web, our observations open a window into important middle-coronal processes that appear to play a key role in driving the structured slow solar wind.

Ultrafast Dynamics of Demagnetization in FeMn/MnGa Bilayer Nanofilm Structures via Phonon Transport.

Superdiffusive spin transport has been proposed as a new mechanism of ultrafast demagnetization in layered magnetic nanostructures and demonstrated experimentally. However, it is unknown if it is possible for phonon transport to occur and manipulate ultrafast demagnetization. Here, we explore the ultrafast dynamics of demagnetization of an antiferromagnet/ferromagnet bilayer nanostructure, of a FeMn/MnGa bilayer film prepared by molecular beam epitaxy. Ultrafast dynamics of a two-step demagnetization were observed through the time-resolved magneto-optical Kerr effect. The first-step fast component of the two-step demagnetization occurred within ~200 fs, while the second-step slow component emerged in a few tens of picoseconds. For a single MnGa film, only the ultrafast dynamics of the first-step fast demagnetization were observed, revealing that the second-step slow demagnetization originates from interlayer phonon transport. A four-temperature model considering phonon transport was developed and used to effectively reproduce the observed ultrafast dynamics of two-step demagnetization. Our results reveal the effect of phonon transport on demagnetization for the first time and open up a new route to manipulate ultrafast demagnetization in layered magnetic structures.

Priming exercise accelerates oxygen uptake kinetics during high-intensity cycle exercise in middle-aged individuals with type 2 diabetes.

Background: The primary phase time constant of pulmonary oxygen uptake kinetics ( τ p) during submaximal efforts is longer in middle-aged people with type 2 diabetes (T2D), partly due to limitations in oxygen supply to active muscles. This study examined if a high-intensity "priming" exercise (PE) would speed τ p during a subsequent high-intensity cycling exercise in T2D due to enhanced oxygen delivery. Methods: Eleven (4 women) middle-aged individuals with type 2 diabetes and 11 (4 women) non-diabetic controls completed four separate cycling bouts each starting at an 'unloaded' baseline of 10W and transitioning to a high-intensity constant-load. Two of the four cycling bouts were preceded by priming exercise. The dynamics of pulmonary and muscle deoxygenation (i.e. deoxygenated haemoglobin and myoglobin concentration [HHb + Mb]), were calculated from breath-by-breath and near-infrared spectroscopy data at the vastus lateralis, respectively. Results: At baseline τ p, was slower (p < 0.001) in the type 2 diabetes group (48 ± 6s) compared to the control group (34 ± 2s) but priming exercise significantly reduced τ p (p < 0.001) in type 2 diabetes (32 ± 6s) so that post priming exercise it was not different compared with controls (34 ± 3s). Priming exercise reduced the amplitude of the slow component (As) in both groups (type 2 diabetes: 0.26 ± 0.11 to 0.16 ± 0.07L/min; control: 0.33 ± 0.13 to 0.25 ± 0.14L/min, p < 0.001), while [HHb + Mb] kinetics remained unchanged. Conclusion: These results suggest that in middle-aged men and women with T2D, PE speeds τ p likely by a better matching of O2 delivery to utilisation and reduces the As during a subsequent high-intensity exercise.

Pedalling Cadence Affects V̇ o2 Kinetics in Severe-Intensity Exercise.

Hill, DW and Vingren, JL. Pedalling cadence affects V̇ o2 kinetics in severe-intensity exercise. J Strength Cond Res 37(6): 1211-1217, 2023-The purpose was to investigate the effects of pedalling cadence on V̇ o2 kinetics in severe-intensity cycling exercise. This question is pertinent to exercise testing, where cadence is an important (and often confounding) variable, and to performance, where V̇ o2 kinetics determines the initial reliance upon anaerobic reserves. Eighteen university students performed tests to exhaustion at 241 ± 31 W, using cadences of 60, 80, and 100 rev·min -1 . V̇ o2 data were fitted to a 2-component model (primary phase + slow component). Responses during the 3 tests were compared using a repeated-measures analysis of variance, with significance at p < 0.05. The mean response time of the primary phase of the V̇ o2 response (time to reach 63% of the response) was progressively smaller (response was faster) at higher cadences (37 ± 4 seconds at 60 rev·min -1 , 32 ± 5 seconds at 80 rev·min -1 , 27 ± 4 seconds at 100 rev·min -1 ), and there was a concomitantly faster heart rate response. In addition, the time delay before the slow component was shorter, the amplitude of the primary phase was greater, and the amplitude of the slow component was smaller at the higher cadence. The results suggest that pedalling cadence itself-and not just the higher metabolic demand associated with higher cadences-may be responsible for differences in temporal characteristics (time delays, time constants) of the primary and slow phases of the V̇ o2 response. Exercise scientists must consider, and coaches might apply, the relationship between V̇ o2 kinetics and pedalling cadence during exercise testing.

Similar Slow Component of Oxygen Uptake and Ventilatory Efficiency between an Aerobic Dance Session on an Air Dissipation Platform and a Constant-Load Treadmill Test in Healthy Women.

There is a lack of evidence about the slow component of oxygen consumption (V.O2sc) and ventilatory efficiency (slope VE·VCO2−1) during an aerobic dance (AD) session on an air dissipation platform (ADP) despite the key role played in endurance exercises. This research was designed to assess V.O2sc, ventilatory efficiency, and blood lactate concentration by comparing two exercise modes: AD session on an ADP versus treadmill test at a constant-load intensity of the first ventilatory threshold (VT1). In the first session, an incremental treadmill test was completed. In sessions 2 and 3, the participants were randomly assigned to the AD session on an ADP or to a treadmill constant-load test at VT1 intensity to determine their cardioventilatory responses. In addition, their blood lactate levels and ratings of perceived exertion (RPE, CR-10) were evaluated. No significant differences were found between the constant-load treadmill test and AD session on an ADP with respect to V.O2sc, VE VCO2−1 slope, and RPE (p > 0.05). Higher blood lactate concentrations were observed in an AD session on an ADP than in a constant-load treadmill test at 10 min (p = 0.003) and 20 min (p < 0.001). The two different exercise modalities showed similar V.O2sc and VE·VCO2−1 slope, even though the blood lactate concentrations were different.

In vitro recording of muscle activity induced by high intensity laser optogenetic stimulation using a diamond quantum biosensor

The detection of physiological activity at the microscopic level is key for understanding the function of biosystems and relating this to their physical structure. Current sensing methods for in vitro study of living tissue often rely on invasive probes to stimulate and detect activity, bearing the risk of inducing damage in the target system. In recent years, a new type of quantum sensor based on color centers in diamond has begun to offer the possibility to instead passively sense and image living biological systems. Here, we use such a sensor to realize the recording of the biomagnetic field generated by tightly focused, high intensity pulsed laser optogenetic neuromuscular stimulation of extensor digitorum longus muscles, dissected from mice and kept alive in carbogenated solution. Recordings captured a compound action potential response and a slow signal component, which we seek to explain using a detailed model of the biological system. We show proof-of-principle experimental recording of localized neuromuscular activity from the laser stimulation site without photovoltaic or fluorescence artifacts associated with alternative techniques. Our work represents a further step toward passive sensing and imaging at the microscopic level with quantum sensing, enabling further research into mapping of neural activity and intracellular processes.

Less is more: A simple methyl-TROSY based pulse scheme offers improved sensitivity in applications to high molecular weight complexes

The HMQC pulse sequence and variants thereof have been exploited in studies of high molecular weight protein complexes, taking advantage of the fact that fast and slow relaxing magnetization components are sequestered along two distinct magnetization transfer pathways. Despite the simplicity of the HMQC scheme an even shorter version can be designed, based on elimination of the terminal refocusing period, as a further means of increasing signal. Here we present such an experiment, and show that significant sensitivity gains, in some cases by factors of two or more, are realized in studies of proteins varying in molecular masses from 100 kDa to 1 MDa.

Testing the accuracy of OSL and pIR IRSL dating of young geoarchaeological sediments in coastal Peru

Luminescence dating of late Quaternary sediments in Peru is challenging, especially on the Peruvian coast. Earlier studies have shown that quartz grains often exhibit a thermally unstable, medium signal that caused the underestimation of Optically Stimulated Luminescence (OSL) ages. InfraRed Stimulated Luminescence (IRSL) dating has shown to produce more reliable ages, depending, amongst other factors, on the age model (Central or Minimum Age Model), and the IRSL signal. IRSL dating of geoarchaeological sediments has, however, hardly been carried out, let along validated, against an independent age dataset. This dating approach is, nonetheless, the only promising way to date the geological substrate in which many of Peru's archaeological sites are buried. Peru contains some of the oldest and most important archaeological heritage sites, yet not much is known of the environmental context in which many of its early civilizations prospered. A better understanding of which luminescence method works best could therefore help in a better understanding of the geological-stratigraphical context of many of Peru's sites. To investigate this matter more fully, we compared the luminescence dating results of seven sediment samples from the top layer of the Lima alluvial fan and from geoarchaeological layers of the Maranga Complex (San Miguel, Lima), with an independent dataset of sixteen 14 C ages. Our results showed that the quartz OSL ages always underestimated the expected ages due to a signal dominated by medium and slow components, and that the post-IR IRSL 225 (pIR IRSL 225 ) and IRSL 50 ages of K-feldspars, on basis of the Central Age Model (CAM), always overestimated the expected ages. The Minimum Age Model (MAM) on the other hand, correctly predicted the expected ages for the early Holocene, Lima alluvial fan sediments using the pIR IRSL 225 signal of K-feldspars, and the late Holocene, geoarchaeological ages using the IRSL 50 signal.

Cross-loop Propagation of a Quasiperiodic Extreme-ultraviolet Wave Train Triggered by Successive Stretching of Magnetic Field Structures during a Solar Eruption

Solar extreme-ultraviolet (EUV) waves generally refer to large-scale disturbances propagating outward from sites of solar eruptions in EUV imaging observations. Using the recent observations from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we report a quasiperiodic wave train propagating outward at an average speed of ∼308 km s−1. At least five wave fronts can be clearly identified with the period being ∼120 s. These wave fronts originate from the coronal loop expansion, which propagates with an apparent speed of ∼95 km s−1, about 3 times slower than the wave train. In the absence of a strong lateral expansion, these observational results might be explained by the theoretical model of Chen et al., which predicted that EUV waves may have two components: a faster component that is a fast-mode magnetoacoustic wave or shock wave and a slower apparent front formed as a result of successive stretching of closed magnetic field lines. In this scenario, the wave train and the successive loop expansion we observed likely correspond to the fast and slow components in the model, respectively.

Photo response of Co-doped BaFe2As2 meander micron line

We report on the response of Ba122:Co meander micron line structures to pulsed 635 nm laser radiation. A 75 nm thick Ba122:Co film was patterned into 2 µm wide and 2.4 mm long meander micron line by a standard photolithographic process and dry etching in an argon ion-milling techniques. The Ba122:Co meander micron line show Tconset = 25.9 K and a critical current density of up to 1.7 × 106 A/cm2 at T = 15 K. The I-V properties of the sample show hysteretic current-voltage characteristics over a wide range of temperatures (5–15 K). The photo response of Ba122:Co meander micron line was studied at temperatures of 5 K and 15 K . At 15 K with Ib = 0.9Ic = 2.40 mA, the pulse had a fast component with a rise time of 1.3 ns and a slower component with a fall time of 15.5 ns, making Ba122:Co a strong competitor in the development of high-temperature superconducting photon detectors.

Membrane retrieval after Immediately Releasable Pool (IRP) exocytosis is produced by dynamin-dependent and dynamin-independent/protein kinase C-dependent mechanisms.

The importance of the immediately releasable pool (IRP) of vesicles was proposed to reside in the maintenance of chromaffin cell secretion during the firing of action potentials at basal physiological frequencies. To accomplish this duty, IRP should be replenished as a function of time. We have previously reported that an action potential-like stimulus (APls) triggers the release of ~50% IRP, followed by a fast dynamin-dependent endocytosis and an associated rapid replenishment process. In this work, we investigated the endocytosis and IRP replenishment produced after the exocytosis of variable IRP fractions in mice primary chromaffin cell cultures. Exocytosis and endocytosis were estimated by membrane capacitance measurements obtained in patch-clamped cells. In addition to the dynamin-dependent fast endocytosis activated after the application of APls or 5ms squared depolarizations, we found that depolarizations lasting 25-50 ms, which release >80% of IRP, are related with a fast dynamin-independent, Ca2+ - and protein kinase C (PKC)-dependent endocytosis (time constant <1s). PKC inhibitors, such as staurosporine, bisindolylmaleimide XI, PKC 19-31 peptide, and prolonged treatments with high concentrations of phorbol esters, reduced and decelerated this endocytosis. Additionally, we found that the inhibition of PKC also abolished a slow component of replenishment (time constant ~8s) observed after total IRP exocytosis. Therefore, our results suggest that PKC contributes to the coordination of membrane retrieval and vesicle replenishment mechanisms that occur after the complete exocytosis of IRP.

Decay times of atmospheric acoustic–gravity waves after deactivation of wave forcing

Abstract. High-resolution numerical simulations of non-stationary, nonlinear acoustic–gravity waves (AGWs) propagating upwards from surface wave sources are performed for different temporal intervals relative to activation and deactivation times of the wave forcing. After activating surface wave sources, amplitudes of AGW spectral components reach a quasi-stationary state. Then the surface wave forcing is deactivated in the numerical model, and amplitudes of vertically traveling AGW modes quickly decrease at all altitudes due to discontinuations of the upward propagation of wave energy from the wave sources. However, later the standard deviation of residual and secondary wave perturbations experiences a slower quasi-exponential decrease. High-resolution simulations allowed, for the first time, for the estimation of the decay times of this wave noise produced by slow residual, quasi-standing and secondary AGW spectral components, which vary between 20 and 100 h depending on altitude and the rate of wave source activation and deactivation. The standard deviations of the wave noise are larger for the case of sharp activation and deactivation of the wave forcing compared to the steep processes. These results show that transient wave sources may create long-lived wave perturbations, which can form a background level of wave noise in the atmosphere. This should be taken into account in parameterizations of atmospheric AGW impacts.

Spontaneous variability predicts compensative motor response in vocal pitch control

Our motor system uses sensory feedback to keep desired performance. From this view, motor fluctuation is not simply ‘noise’ inevitably caused in the nervous system but would play a role in generating variations to explore better outcomes via sensory feedback. Vocalization system offers a good model for studying such sensory-motor interactions since we regulate vocalization by hearing our own voice. This behavior is typically observed as compensatory responses in vocalized pitch, or fundamental frequency (fo), when artificial fo shifts were induced in the auditory feedback. However, the relationship between adaptive regulation and motor exploration in vocalization has remained unclear. Here we investigated behavioral variability in spontaneous vocal fo and compensatory responses against fo shifts in the feedback, and demonstrated that larger spontaneous fluctuation correlates with greater compensation in vocal fo. This correlation was found in slow components (≤ 5 Hz) of the spontaneous fluctuation but not in fast components (between 6 and 30 Hz), and the slow one was amplified during the compensatory responses. Furthermore, the compensatory ratio was reduced when large fo shifts were applied to the auditory feedback, as if reflecting the range of motor exploration. All these findings consistently suggest the functional role of motor variability in the exploration of better vocal outcomes.

Optimal noise level for coding with tightly balanced networks of spiking neurons in the presence of transmission delays.

Neural circuits consist of many noisy, slow components, with individual neurons subject to ion channel noise, axonal propagation delays, and unreliable and slow synaptic transmission. This raises a fundamental question: how can reliable computation emerge from such unreliable components? A classic strategy is to simply average over a population of N weakly-coupled neurons to achieve errors that scale as . But more interestingly, recent work has introduced networks of leaky integrate-and-fire (LIF) neurons that achieve coding errors that scale superclassically as 1/N by combining the principles of predictive coding and fast and tight inhibitory-excitatory balance. However, spike transmission delays preclude such fast inhibition, and computational studies have observed that such delays can cause pathological synchronization that in turn destroys superclassical coding performance. Intriguingly, it has also been observed in simulations that noise can actually improve coding performance, and that there exists some optimal level of noise that minimizes coding error. However, we lack a quantitative theory that describes this fascinating interplay between delays, noise and neural coding performance in spiking networks. In this work, we elucidate the mechanisms underpinning this beneficial role of noise by deriving analytical expressions for coding error as a function of spike propagation delay and noise levels in predictive coding tight-balance networks of LIF neurons. Furthermore, we compute the minimal coding error and the associated optimal noise level, finding that they grow as power-laws with the delay. Our analysis reveals quantitatively how optimal levels of noise can rescue neural coding performance in spiking neural networks with delays by preventing the build up of pathological synchrony without overwhelming the overall spiking dynamics. This analysis can serve as a foundation for the further study of precise computation in the presence of noise and delays in efficient spiking neural circuits.

Fear memory in humans is consolidated over time independently of sleep

Fear memories can be altered after acquisition by processes, such as fear memory consolidation or fear extinction, even without further exposure to the fear-eliciting stimuli, but factors contributing to these processes are not well understood. Sleep is known to consolidate, strengthen, and change newly acquired declarative and procedural memories. However, evidence on the role of time and sleep in the consolidation of fear memories is inconclusive. We used highly sensitive electrophysiological measures to examine the development of fear-conditioned responses over time and sleep in humans. We assessed event-related brain potentials (ERP) in 18 healthy, young individuals during fear conditioning before and after a 2-hour afternoon nap or a corresponding wake interval in a counterbalanced within-subject design. The procedure involved pairing a neutral tone (CS+) with a highly unpleasant sound. As a control, another neutral tone (CS−) was paired with a neutral sound. Fear responses were examined before the interval during a habituation phase and an acquisition phase as well as after the interval during an extinction phase and a reacquisition phase. Differential fear conditioning during acquisition was evidenced by a more negative slow ERP component (stimulus-preceding negativity) developing before the unconditioned stimulus (loud noise). This differential fear response was even stronger after the interval during reacquisition compared with initial acquisition, but this effect was similarly pronounced after sleep and wakefulness. These findings suggest that fear memories are consolidated over time, with this effect being independent of intervening sleep.

Amplitude and frequency modulation of subthalamic beta oscillations jointly encode the dopaminergic state in Parkinson’s disease

Brain states in health and disease are classically defined by the power or the spontaneous amplitude modulation (AM) of neuronal oscillations in specific frequency bands. Conversely, the possible role of the spontaneous frequency modulation (FM) in defining pathophysiological brain states remains unclear. As a paradigmatic example of pathophysiological resting states, here we assessed the spontaneous AM and FM dynamics of subthalamic beta oscillations recorded in patients with Parkinson’s disease before and after levodopa administration. Even though AM and FM are mathematically independent, they displayed negatively correlated dynamics. First, AM decreased while FM increased with levodopa. Second, instantaneous amplitude and instantaneous frequency were negatively cross-correlated within dopaminergic states, with FM following AM by approximately one beta cycle. Third, AM and FM changes were also negatively correlated between dopaminergic states. Both the slow component of the FM and the fast component (i.e. the phase slips) increased after levodopa, but they differently contributed to the AM-FM correlations within and between states. Finally, AM and FM provided information about whether the patients were OFF vs. ON levodopa, with partial redundancy and with FM being more informative than AM. AM and FM of spontaneous beta oscillations can thus both separately and jointly encode the dopaminergic state in patients with Parkinson’s disease. These results suggest that resting brain states are defined not only by AM dynamics but also, and possibly more prominently, by FM dynamics of neuronal oscillations.

Response to “complexities of defining the bioenergetic efficiency and VO 2 slow component of skeletal muscle contraction”

Response to “complexities of defining the bioenergetic efficiency and <scp> VO ₂ </scp> slow component of skeletal muscle contraction”

(Invited) Alkaline Membrane Electrolyzers: Catalysts, Degradation Mechanisms, and Materials Engineering for Performance and Durability

Commercialized membrane electrolyzers use acidic proton exchange membranes (PEMs). These systems offer high performance but require the use of expensive precious-metal catalysts such as IrO2 and Pt that are nominally stable under the locally acidic conditions of the ionomer. Alkaline-exchange-membrane (AEM) electrolyzers in principle offer the performance of commercialized PEM electrolyzers with the ability to use earth-abundant catalysts and inexpensive bipolar plate materials. I will present our fundamental work in understanding earth-abundant water-oxidation catalysts, including the use of integrated reference-electrode device architectures and cross-sectional materials analysis, as well as progress in building high-performance AEM electrolyzers. Baseline systems operate at 1 A·cm-2 in pure water feed at < 1.9 V at a moderate temperature of ~70 °C using either IrO2 or Co3O4 anode catalyst layers, PiperION alkaline ionomers, and stainless steel porous transport layers. These devices, however, degrade rapidly compared to PEM electrolyzers. The voltage profile corresponding to degradation has intial fast (~10 mV/h) and steady-state slow components (~1 mV/h), which we link to chemical and structural changes in the ionomer catalyst reactive zone. I will discuss these processes in electrolyzer devices and in model systems that are correlated with this performance loss, as well as present promising new strategies we have developed to mitigate degradation using novel ionomers and electrode catalyst compositions and architectures. Figure 1

Buoyancy-modulated Lagrangian drift in wavy-walled vertical channels as a model problem to understand drug dispersion in the spinal canal.

This paper investigates flow and transport in a slender wavy-walled vertical channel subject to a prescribed oscillatory pressure difference between its ends. When the ratio of the stroke length of the pulsatile flow to the channel wavelength is small, the resulting flow velocity is known to include a slow steady-streaming component resulting from the effect of the convective acceleration. Our study considers the additional effect of gravitational forces in configurations with a non-uniform density distribution. Specific attention is given to the slowly evolving buoyancy-modulated flow emerging after the deposition of a finite amount of solute whose density is different from that of the fluid contained in the channel, a relevant problem in connection with drug dispersion in intrathecal drug delivery (ITDD) processes, involving the injection of the drug into the cerebrospinal fluid that fills the spinal canal. It is shown that when the Richardson number is of order unity, the relevant limit in ITDD applications, the resulting buoyancy-induced velocities are comparable to those of steady streaming. As a consequence, the slow time-averaged Lagrangian motion of the fluid, involving the sum of the Stokes drift and the time-averaged Eulerian velocity, is intimately coupled with the transport of the solute, resulting in a slowly evolving problem that can be treated with two-time-scale methods. The asymptotic development leads to a time-averaged, nonlinear integro-differential transport equation that describes the slow dispersion of the solute, thereby circumventing the need to describe the small concentration fluctuations associated with the fast oscillatory motion. The ideas presented here can find application in developing reduced models for future quantitative analyses of drug dispersion in the spinal canal.

Analysis of multiscale methods for stochastic dynamical systems driven by [formula omitted]-stable processes

In this paper, we firstly analyze the strong convergence of projective integration method for multiscale stochastic dynamical systems driven by α-stable processes, which is used to estimate the effect that the fast components have on slow ones. Then we obtain the pth moment error bounds between the solution of slow component produced by projective integration method and the solution of effective system with p∈1,α. Finally, we corroborate our analytical results through a specific numerical example.