Sequential Trains Research Articles

RRAT J1913+1330: An Extremely Variable and Puzzling Pulsar

Rotating radio transients (RRATs) are neutron stars that emit sporadic radio bursts. We detected 1955 single pulses from RRAT J1913+1330 using the 19 beam receiver of the Five-hundred-meter Aperture Spherical radio Telescope. These pulses were detected in 19 distinct clusters, with 49.4% of them occurring with a waiting time of one rotation period. The energy distribution of these individual pulses exhibited a wide range, spanning 3 orders of magnitude, reminiscent of repeating fast radio bursts (FRBs). Furthermore, we observed abrupt variations in pulse profile, width, peak flux, and fluence between adjacent sequential pulses. These findings suggest that this RRAT could be interpreted as a pulsar with extreme pulse-to-pulse modulation. The presence of sequential pulse trains during active phases, along with significant pulse variations in profile, fluence, flux, and width, should be intrinsic to a subset of RRATs. Our results indicate that J1913+1330 represents a peculiar source that shares certain properties with populations of nulling pulsars, giant pulses, and FRBs from different perspectives. The dramatic pulse-to-pulse variation observed in J1913+1330 could be attributed to unstable pair creation above the polar cap region and the variation of the site where streaming pairs emit coherently. Exploring a larger sample of RRATs exhibiting similar properties to J1913+1330 has the potential to significantly advance our understanding of pulsars, RRATs, and FRBs.

Neural effects of TMS trains on the human prefrontal cortex

How does a train of TMS pulses modify neural activity in humans? Despite adoption of repetitive TMS (rTMS) for the treatment of neuropsychiatric disorders, we still do not understand how rTMS changes the human brain. This limited understanding stems in part from a lack of methods for noninvasively measuring the neural effects of a single TMS train—a fundamental building block of treatment—as well as the cumulative effects of consecutive TMS trains. Gaining this understanding would provide foundational knowledge to guide the next generation of treatments. Here, to overcome this limitation, we developed methods to noninvasively measure causal and acute changes in cortical excitability and evaluated this neural response to single and sequential TMS trains. In 16 healthy adults, standard 10 Hz trains were applied to the dorsolateral prefrontal cortex in a randomized, sham-controlled, event-related design and changes were assessed based on the TMS-evoked potential (TEP), a measure of cortical excitability. We hypothesized that single TMS trains would induce changes in the local TEP amplitude and that those changes would accumulate across sequential trains, but primary analyses did not indicate evidence in support of either of these hypotheses. Exploratory analyses demonstrated non-local neural changes in sensor and source space and local neural changes in phase and source space. Together these results suggest that single and sequential TMS trains may not be sufficient to modulate local cortical excitability indexed by typical TEP amplitude metrics but may cause neural changes that can be detected outside the stimulation area or using phase or source space metrics. This work should be contextualized as methods development for the monitoring of transient noninvasive neural changes during rTMS and contributes to a growing understanding of the neural effects of rTMS.

Forming-Free Tunable Analog Switching in WOx/TaOx Heterojunction for Emulating Electronic Synapses.

In this work, the sputtered deposited WOx/TaOx switching layer has been studied for resistive random-access memory (RRAM) devices. Gradual SET and RESET behaviors with reliable device-to-device variability were obtained with DC voltage sweep cycling without an electroforming process. The memristor shows uniform switching characteristics, low switching voltages, and a high RON/ROFF ratio (~102). The transition from short-term plasticity (STP) to long-term potentiation (LTP) can be observed by increasing the pulse amplitude and number. Spike-rate-dependent plasticity (SRDP) and paired-pulse facilitation (PPF) learning processes were successfully emulated by sequential pulse trains. By reducing the pulse interval, the synaptic weight change increases due to the residual oxygen vacancy near the conductive filaments (CFs). This work explores mimicking the biological synaptic behavior and further development for next-generation neuromorphic applications.

Quasi‐biennial oscillation impacts on Madden–Julianoscillation‐associatedtropical–extratropical interactions and Kelvin waves

AbstractSeveral recent works have demonstrated that the Madden–Julian oscillation (MJO) shows more variance in tropical convection and wind during the easterly phase of stratospheric wind in the quasi‐biennial oscillation (QBO). Some of these works have shown that reduced variance during the westerly QBO is associated with fewer repeating cycles of events. This article applies a modulation linear regression algorithm to assess changes in the global atmospheric circulation structure for December–February MJO signals tested when time‐smoothed 50 hPa winds are easterly or westerly at 10 m·s−1. Results show pronounced differences in the associated extratropical upper tropospheric Rossby wave response between the two QBO states, along with a comparatively lower fraction of total eastward wave energy being consistent with Kelvin waves approaching the Indian basin from the west during the westerly QBO. Instead, westerly QBO appears to favour stronger equatorward‐moving extratropical wave precursors across the Western Hemisphere and Eurasia. The results suggest the hypothesis that more dependence on extratropical waves during the westerly QBO may reduce the reliability of the MJO to form sequential trains during the westerly QBO.

Re-igniting the afterglow plasma column of an AC powered gliding arc discharge in atmospheric-pressure air

The stability and re-ignition characteristics of the plasma column of an alternating current (AC) powered gliding arc discharge operating in atmospheric-pressure air were investigated for better plasma-mode controlling and optimized applications. By modulating the AC power supply and the air flow field, the states of afterglow plasma column were varied. When pulsating the AC power supply sequence, re-ignitions of the afterglow columns were introduced and their characteristics were studied using simultaneous high-speed photography and electrical measurements. Two re-ignition types were observed in the afterglow column with different decay times (the temporal separation of two sequential pulsed AC power trains). For a short decay time (<200 μs at 10 l/min air flow), the afterglow column can be recovered mildly without current spikes, which is called a glow re-ignition event. If the decay time is so long that the electric field strength becomes larger than 120 kV/m, the re-ignition event occurs with current spikes and bright emissions, which is called a spark re-ignition event. A quasi-equilibrium model is proposed to estimate the chemical compositions in the plasma column and to explain the observed phenomena. It infers that the chemical dissociation and ionization processes enhanced by vibrationally excited nitrogen molecules are dominating in the afterglow plasmas and thereby the electrons can survive a long time to keep the conductivity of the afterglow column, forming a glow re-ignition event. Whereas under large electric field strength (>120 kV/m), the electron impact ionization becomes dominant to trigger the spark re-ignition event.

Investigation of the multilevel capability of TiN/Ti/HfO2/W resistive switching devices by sweep and pulse programming

Multilevel states are clearly distinguished in TiN/Ti/HfO2/W RRAM devices by programming sequential voltage ramps and trains of pulses. It has been shown that the filamentary conductance has a continuous dependence on the current compliance employed during the SET process and the maximum voltage applied during the RESET process. The LRS conductance is determined by the current compliance, while the HRS is given by the RESET pulse amplitude. The obtained results suggest that the studied devices can be employed as electronic synaptic devices in neuromorphic circuits.

Characteristics of thermally induced acoustic emission from nanoporous silicon device under full digital operation

The resonance-free frequency response of the thermo-acoustic emission is demonstrated under a full digital drive. The device is composed of a thin-film heater electrode, a nano-porous silicon layer, and a single-crystalline silicon wafer. When sequential electrical pulse trains converted by the density modulation of an analog signal are introduced into the heater electrode, a significant sound pressure is reproduced with a sufficiently low distortion. The characteristic output behaviour in the audible ultrasonic band is clarified in either open- or closed-space. The advantageous features of thermally induced sound emission and its underlying physics have been made clear.

Electrical colonic stimulation reduces mean transit time in a porcine model

Electrical stimulation is a new way to treat digestive disorders such as constipation. Colonic propulsive activity can be triggered by battery operated devices. This study aimed to demonstrate the effect of direct electrical colonic stimulation on mean transit time in a chronic porcine model. The impact of stimulation and implanted material on the colonic wall was also assessed. Three pairs of electrodes were implanted into the caecal wall of 12 anaesthetized pigs. Reference colonic transit time was determined by radiopaque markers for each pig before implantation. It was repeated 4 weeks after implantation with sham stimulation and 5 weeks after implantation with electrical stimulation. Aboral sequential trains of 1-ms pulse width (10 V; 120 Hz) were applied twice daily for 6 days, using an external battery operated stimulator. For each course of markers, a mean value was computed from transit times obtained from individual pig. Microscopic examination of the caecum was routinely performed after animal sacrifice. A reduction of mean transit time was observed after electrical stimulation (19 +/- 13 h; mean +/- SD) when compared to reference (34 +/- 7 h; P = 0.045) and mean transit time after sham stimulation (36 +/- 9 h; P = 0.035). Histological examination revealed minimal chronic inflammation around the electrodes. Colonic transit time measured in a chronic porcine model is reduced by direct sequential electrical stimulation. Minimal tissue lesion is elicited by stimulation or implanted material. Electrical colonic stimulation could be a promising approach to treat specific disorders of the large bowel.

Simulation of the reversal of neuromuscular block by sequestration of the free molecules of the muscle relaxant

The study examined in simulations the interaction between a muscle relaxant and an antagonist that binds the free molecules of the relaxant, as experimentally demonstrated for rocuronium and sugammadex. The hypothetical muscle relaxant D and the hypothetical antagonist X were assigned pharmacokinetic properties to define the time course of their concentrations in plasma, and pharmacodynamic properties to define binding of D to either X or the receptors at the motor end plates. D, X, and their complex DX were postulated to diffuse between plasma and the effect compartment. The first and the fourth twitch elicited in sequential trains of four stimuli were evaluated in a model of neuromuscular transmission. The rates of reactions were formulated as differential equations and the equations solved numerically. If the affinity of D for X is comparable to that of D for the postsynaptic receptors, doses of X two to four times larger than the dose of D produce a fast and a complete recovery of the twitches. Smaller doses of X or lower affinities of D for X accomplish a slower and only partial recovery. Additionally, the complete restoration of twitch strength within 2 min after the injection of X requires that X and DX diffuse into the effect compartment. The simulations reveal the physicochemical, pharmacokinetic, and pharmacodynamic properties of an antagonist that restores twitch strength by sequestering the free molecules of the muscle relaxant.

Ca2+-Dependent Activator Protein for Secretion Is Critical for the Fusion of Dense-Core Vesicles with the Membrane in Calf Adrenal Chromaffin Cells

Calcium-dependent activator protein for secretion (CAPS) is a neural/endocrine cell-specific protein that has been shown to function at the Ca(2+)-dependent triggering step of dense-core vesicle (DCV) exocytosis in permeabilized PC12 cells. To evaluate the function of CAPS under physiological conditions, we introduced affinity-purified anti-CAPS IgGs into calf adrenal chromaffin (AC) cells via a patch pipette and tested the kinetics of catecholamine secretion using both amperometric and membrane capacitance techniques. The antibodies reacted with a single major approximately 145 kDa protein in AC cells based on immunoblot analysis. AC cells stimulated with sequential trains of action potentials at 7 Hz resulted in successive secretory episodes of equivalent magnitude. When either of two different anti-CAPS IgGs or their Fab fragments were present, a rapid and progressive inhibition of catecholamine release ensued to a maximum of >80%. The effect was specific because preabsorption of IgGs with the respective antigens ablated the inhibitory effect, and the IgGs had no effect on Ca currents. CAPS immunoneutralization not only reduced the number of amperometric spikes but markedly altered the kinetic characteristics of the residual events. The remaining spikes were much smaller (by 85%) and broader (by approximately 3.5-fold) than those in control cells, suggesting that CAPS plays a role in determining release of vesicle contents via the fusion pore. Anti-CAPS IgGs also slowed the rate of the initial exocytotic capacitance burst, representing the docked-and-primed vesicle pool, by approximately 90% but had no effect on the kinetics of rapid endocytosis. These results suggest that CAPS is a key component regulating the fusion of DCVs to the plasma membrane, and possibly fusion pore dilation, in catecholamine secretion from AC cells.

In vitro measurement of endogenous norepinephrine release from small blood vessels with short stimulation trains

We have previously developed a low-volume perfusion-superfusion system for studying neurotransmitter release in small blood vessels. We now extend this technique to allow for the measurement of neurotransmitter release with short stimulation trains in order to examine modulating factors such as activation of prejunctional receptors or the effects of altered external calcium. Segments of rat tail artery were perfused in the presence of deoxycorticosterone and cocaine (10 −5 M). For short trains, nerves were activated with five sequential trains, each 4 sec in length (total of 160 pulses) at 8 Hz. For long trains, nerves were activated continuously for 3 min for a total of 1440 pulses. Norepinephrine in the perfusate and tissue norepinephrine were quantitated with high-performance liquid chromatography (HPLC) and electrochemical detection. Fractional norepinephrine release was significantly greater with short as compared to long trains when extracellular calcium was maintained at 1.6 mM. When nerves were stimulated with short trains, fractional norepinephrine release was very sensitive to altered extracellular calcium, with a significant decline when extracellular calcium was reduced to 1 mM and a significant increase when extracellular calcium was increased to 5 mM. In contrast, with long-stimulation trains increases or decreases in calcium had no effect on fractional norepinephrine release. This unique method facilitates the study of norepinephrine release with short trains or low-frequency activation and will also make it easier to study presynaptic receptor function as well as interactions between extracellular calcium and presynaptic effectiveness.

Complete assignment of the imino protons of Escherichia coli valine transfer RNA: two-dimensional NMR studies in water.

The imino proton spectrum of Escherichia coli valine tRNA has been studied by two-dimensional nuclear Overhauser effect spectroscopy (NOESY) in H2O solution. The small nuclear Overhauser effects from the imino proton of an internal base pair to the imino protons of each nearest neighbor can be observed as off-diagonal cross-peaks. In this way most of the sequential NOE connectivity trains for all the helices in this molecule can be determined in a single experiment. AU resonances can be distinguished from GC resonances by the AU imino NOE to the aromatic adenine C2-H, thus leading to specific base-pair assignments. In general, the NOESY spectrum alone is not capable of assigning every imino proton resonance even in well-resolved tRNA spectra. Multiple proton peaks exhibit more than two cross-peaks, resulting in ambiguous connectivities, and coupling between protons with similar chemical shifts produces cross-peaks that are incompletely resolved from the diagonal. The sequence of the particular tRNA determines the occurrence of the latter problem, which can often be solved by careful one-dimensional experiments. The complete imino proton assignments of E. coli valine tRNA are presented.

Use of a Teaching Pneumatic Otoscope

To the Editor.— Conventional instruction in otoscopy relies on sequential observations of the tympanic membrane by instructor and student. This method is beset with difficulties, including discomfort for the patient, trauma to the external auditory canal, and the inability of the instructor to be sure that the student is seeing the structures described. Particularly difficult to teach with conventional methods is the skill of pneumatic otoscopy. Students must learn the response of the tympanic membrane to varying pressures of air. This mode of sequential examination trains students poorly; interobserver differences are great.1Teaching operating microscopes used by otolaryngologists obviate these difficulties, but such devices are large, expensive, and usually unavailable in a pediatric clinic or office. At our request, a teaching pneumatic otoscope was designed and manufactured by Welch-Allyn Inc, Skaneateles Falls, NY (Figure). Two viewing ports allow examination simultaneously by two observers. The instructor can demonstrate specific structures,