Exponential Recovery Research Articles

Inhomogeneous magnetization transfer (ihMT) imaging reveals variable recovery profiles of active MS lesions according to size and localization

Abstract This work aims at exploiting the unique myelin specificity of the inhomogeneous magnetization transfer (ihMT) technique to characterize the recovery dynamics of active multiple sclerosis (MS) lesions. IhMT and three other myelin-sensitive techniques, conventional MT, T1-weighted, and diffusion tensor imaging, were applied in a 12-month longitudinal study performed on relapsing-remitting MS patients. An exponential recovery model was used to fit the variations over time of the metrics derived from each MR technique within new active lesions. A principal component analysis was performed on the model parameters obtained for all MR myelin-sensitive techniques across all active lesions of all patients to identify specific recovery profiles. The results show that the recovery profiles of myelin-sensitive MR metrics in active MS lesions vary according to the localization and size of lesions. The distance of lesions from the ventricles is positively associated with the recovery rates of ihMTR and T1w-MPRAGE: the further the lesion is from the ventricles, the higher the recovery rate of these metrics. Lesion size is positively associated with initial loss and negatively associated with final recovery of ihMTR and other MR metrics: small lesions have lower initial loss and greater final recovery of MR metrics than large lesions. Thanks to the specificity of the ihMT technique for myelin, these features can be interpreted in terms of remyelination. This study thus provides longitudinal in vivo support for the pathological observations of higher remyelination in small lesions compared with large ones and faster remyelination in lesions away from the ventricles. These results support the use of ihMT and other measures for quantifying remyelination rates in clinical studies of remyelination therapies.

Research on resilience assessment method of train control on-board system

To address the problem of difficult performance assessment of train control on-board system after recovery from failures, we have proposed a resilience assessment methodology that uses reliability as an indicator of system resilience. Since the system failures are time-dependent, we adopted the Discrete Time Bayesian Network method to obtain the system's reliability before and after failure. Subsequently, we used an exponential recovery model to quantify the system's performance curve during the recovery phase, and finally utilized the resilient triangle area method to quantify its resilience size. Analyzing the CTCS3-300T train control on-board system, we found that the resilience of the system with cold standby redundancy design and hot standby redundancy design were 89.44 % and 87.34 %, respectively, indicating a slight decrease in system performance after recovery from failures compared to pre-failure levels. At that time, it was necessary to adjust operational plans based on actual conditions to avoid greater impact on the railway network. This paper realizes performance resilience of train control on-board system after failure recovery, which can be applied to similar systems and provide theoretical references for realizing intelligent maintenance of the high-speed train.

How Solar Wind Controls the Recovery Phase Morphology of Intense Magnetic Storms

AbstractGeomagnetic storms are critical space weather phenomena resulting from the interaction between the solar wind and the Earth's magnetosphere. However, most studies focus on the main phase of magnetic storms, leaving the morphology of the recovery phase an open question. In this study, we analyze 82 intense magnetic storms with the minimum Dst index ≤ −100 nT between 1995 and 2018, finding that these storms can be classified into two distinct types: one‐stage recovery storms that exhibit a single rapid exponential recovery and two‐stage recovery storms that are characterized by a rapid exponential recovery in the early recovery phase and a slow linear recovery in the later recovery phase. We find that the two‐stage recovery storms are dominant, accounting for approximately 60% of the events. Interestingly, the proportion of two‐stage recovery storms peaks during solar minimum. The two‐stage recovery storms tend to be accompanied by more Alfvén waves with long‐duration and intense southward interplanetary magnetic fields. In addition, we find that the decay rate of the Dst index in the later recovery phase is correlated with the average BZ of the interplanetary magnetic field when the solar wind has a high degree of Alfvénicity. Overall, our results shed new light on the recovery phase morphology of intense magnetic storms and highlight the role of Alfvén waves in this process.

The ORT and the uGMRT pulsar monitoring program: Pulsar timing irregularities & the Gaussian process realisation

Abstract The spin-down law of pulsars is generally perturbed by two types of timing irregularities: glitches and timing noise. Glitches are sudden changes in the rotational frequency of pulsars, while timing noise is a discernible stochastic wandering in the phase, period, or spin-down rate of a pulsar. We present the timing results of a sample of glitching pulsars observed using the Ooty Radio Telescope (ORT) and the upgraded Giant Metrewave Radio Telescope (uGMRT). Our findings include timing noise analysis for 17 pulsars, with seven being reported for the first time. We detected five glitches in four pulsars and a glitch-like event in PSR J1825–0935. The frequency evolution of glitches in pulsars, J0742–2822 and J1740–3015, is presented for the first time. Additionally, we report timing noise results for three glitching pulsars. The timing noise was analysed separately in the pre-glitch and post-glitch regions. We observed an increase in the red noise parameters in the post-glitch regions, where exponential recovery was considered in the noise analysis. Timing noise can introduce ambiguities in the correct evaluation of glitch observations. Hence, it is important to consider timing noise in glitch analysis. We propose an innovative glitch verification approach designed to discern between a glitch and strong timing noise. The novel glitch analysis technique is also demonstrated using the observed data.

Results of 23 yr of Pulsar Timing of PSR J1453-6413

In this paper, we presented the 23.3 yr of pulsar timing results of PSR J1456−6413 based on the observations of Parkes 64 m radio telescope. We detected two new glitches at MJD 57093(3) and 59060(12) and confirmed its first glitch at MJD 54554(10). The relative sizes (Δν/ν) of these two new glitches are 0.9 × 10−9 and 1.16 × 10−9, respectively. Using the “Cholesky” timing analysis method, we have determined its position, proper motion, and two-dimensional transverse velocities from the data segments before and after the second glitch, respectively. Furthermore, we detected exponential recovery behavior after the first glitch, with a recovery timescale of approximately 200 days and a corresponding exponential recovery factor Q of approximately 0.15(2), while no exponential recovery was detected for the other two glitches. More interestingly, we found that the leading component of the integral pulse profile after the second glitch became stronger, while the main component became weaker. Our results will expand the sample of pulsars with magnetosphere fluctuation triggered by the glitch event.

Pulsar glitch in a strangeon star model – III. The recovery

ABSTRACT Strangeon star model has passed various observational tests, such as the massive pulsars and the tidal deformability during binary mergers. Pulsar glitch, as a useful probe for studying the interior structure of pulsars, has also been studied in strangeon star model in our previous papers, including the recovery coefficient, the waiting time of glitches, and glitch activity. In this paper, the recovery process of a glitch is described in the strangeon star model, based on the starquake picture established before (in Paper I). After the starquake, the inner motion of the stellar matter would reduce the tangential pressure in the cracked places at the equatorial plane. The recovery (increase) of the tangential pressure would be achieved by a viscous flow towards the cracked places at equatorial plane, which leads to the exponential recovery of the spin frequency. A uniform viscous flow can reproduce the single exponential decay observed in some glitches, and the viscous time-scale τ and the depth h of the cracking place below the surface can be fitted by the recovery data. It is found that h increases with glitch size Δν/ν, which is expected in the glitch scenario of strangeon stars. The magnitude of the recovery predicted in this recovery model is also consistent with that derived from observations. The single exponential decay reproduced by a uniform viscous flow can be generalized to two or more exponentials by the multicomponent of viscous flows.

Formation damage and improved recovery in kaolinitic high enthalpy gas fields with fabric geological settings

This paper investigates the fines migration and transport in natural gas reservoirs as a function of porous rocks with fabric geological settings. So, an analytical and surface thermodynamic model was developed for high temperature permeable media. Two sets of core flood experiments were conducted under normal (50 °C) and high temperature (150 °C) fluid flow, where the major results revealed that there is an increase in the rock core thermal expansion of 57 (10−6°C−1) and 192 (10−6°C−1) at 50 °C and 150 °C. The rock core underwent a thermal strain to 0.36% and 0.86% under normal and higher temperature conditions. At 50 °C the pressure stabilized to 20 psi and 50 psi was recorded as the peak pressure under 150 °C rock temperature. The fines concentration under higher temperature is significantly higher than the normal rock temperature and yielded maximum up to 77.28 ppm. The rock permeability exhibited a linear and stabilized decline, but at higher temperature new surface energies was created in the rock core and as a result, the reservoir permeability begun to rebound. Microstructural images revealed that the kaolinite clay fine particle under 50 °C has a platelet structure and has multiple straining mechanism. Whereas, under higher temperature the clay fines have transcended to compaction over the rock surface fabrics. Exponential gas recovery of 15% and 25% was observed for both 50 °C and 150 °C cases. In the former case, a linear growth rate to 25% was noted and then gradually it fell to 12.9%. While, in the latter case the gas recovery rate climbed to 33.7% and stabilized, which indicates that the gas recovery rate was monotonous. The experimental and analytical models have been verified using multiple linear regression method and the model's outcome revealed an excellent agreement whose R2 values were found to be 0.9997 and 0.9995.

Improved response model of a superconducting nanowire array for high photon count rate communication

In high-speed photon-counting communication where the slot duration is close to the scale of detector reset time, the detection efficiency recovery characteristics of superconducting nanowire single photon detector (SNSPD) become the key factors affecting counting and communication performance. We introduced the nonlinear detection efficiency recovery model derived from the kinetic inductance model combined with the nonlinear efficiency-current relationship into the pulse position modulation (PPM) optical communication system based on the SNSPD array, and studied the impact of the recovery characteristics on the counting and communication performance of the system. On this basis, we introduce the efficiency recovery model into the correction of the channel logarithmic likelihood ratio (LLR) to estimate the SNR of each slot more accurately. Relevant results show that compared with the existing Poisson channel model, fixed deadtime model and detection efficiency exponential recovery model, this modification combined with FEC can provide the best decoding performance, especially in scenarios with high PPM order, small array pixel number and strong noise level. Besides, the nonlinear detection efficiency recovery model also reflects the best consistency with the experimental measurements of the SNSPD array in terms of response count rates near saturation.

Calibrated Electrochemical Impedance Spectroscopy and Time‐Domain Measurements of a 7 kWh Automotive Lithium‐Ion Battery Module with 396 Cylindrical Cells

AbstractA 7 kWh automotive battery module with 396 interconnected cells was tested with electrochemical impedance spectroscopy (EIS) and time‐domain pulsing over 260 charge‐discharge cycles. An EIS calibration workflow was developed for low complex impedance values in a frequency range of 1 kHz to 50 mHz. Significant corrections on the resistance and the reactance were obtained from the calibration, particularly at frequencies above 100 Hz. Equivalent circuit parameters were extracted from the EIS spectra and the pulse response and investigated with respect to the cycle number and state‐of‐charge (SoC). Fit parameters were robustly extracted including Rsol, Rct, and L from EIS, and R0, τ1 and τ2 from time‐domain pulsing. The ohmic resistance decreased over the cycling number indicating an enhanced wetting of the electrodes. Charge transfer resistance Rct showed a monotonic increase over the cycles related to cell ageing. From the charge and discharge pulses, the ohmic resistance R0 was determined from the instantaneous voltage step of the recovery pulse, while the two time constants τ1 and τ2 correspond to the slower exponential recovery phase. R0 from the time‐domain showed a similar trend as Rsol plus a contribution of Rct from EIS. Overall, we show that calibrated EIS and time‐domain pulsing are efficient methods to gain insights into the electrochemical processes related to different SoCs and the cycling ageing of battery modules and packs.

Detection of 16 Small Glitches in Nine Pulsars

Pulsar timing measurements with a 26 m radio telescope at Nanshan between 2000 and 2014 were used to search for glitch events. The data span of nine pulsars ranges from 11.6 to 14.2 yr, and 16 new glitch events were identified in nine pulsars. Glitch parameters were determined through fitting the timing residuals data. All 16 glitches have a small fractional size. Six new glitches have been detected in PSR J1833−0827, making it another frequent glitching pulsar. Some of the 16 glitches may experience exponential or linear recovery, but it is unlikely for us to make further analyses with the large gap in the data set. All the glitch rates obtained from Nanshan are higher than that from Jodrell Bank Observatory. The small glitch size and high glitch rate could possibly attribute to the high observation cadence.

Performance-Boosting Attitude Control for 2-DOF Helicopter Applications via Surface Stabilization Approach

This study solves the attitude stabilization problem of 2-degree-of-freedom (2-DOF) helicopters by robustly assigning the variable-performance to the closed-loop system in the presence of the model-plant mismatches and load variations. The proposed approach reformulates the original problem to a surface stabilization one which yields three contributions: a) the proposed attitude velocity observer forms a conventional Luenberger-type observer incorporating the parameter-independence and estimation gains specifically designed for causing the pole-zero cancellation, b) the pole-zero cancellation velocity control loop makes it possible to accomplish the surface stabilization task with the first-order closed-loop order, and c) the closed-loop analysis results demonstrate the attractive properties of the exponential performance recovery and convergence. The effectiveness of the proposed technique is verified using the experimental platform provided by the Quanser AERO.

Trap-state mapping to model GaN transistors dynamic performance

Trapping phenomena degrade the dynamic performance of wide-bandgap transistors. However, the identification of the related traps is challenging, especially in presence of non-ideal defects. In this paper, we propose a novel methodology (trap-state mapping) to extract trap parameters, based on the mathematical study of stretched exponential recovery kinetics. To demonstrate the effectiveness of the approach, we use it to identify the properties of traps in AlGaN/GaN transistors, submitted to hot-electron stress. After describing the mathematical framework, we demonstrate that the proposed methodology can univocally describe the properties of the distribution of trap states. In addition, to prove the validity and the usefulness of the model, the trap properties extracted mathematically are used as input for TCAD simulations. The results obtained by TCAD closely match the experimental transient curves, thus confirming the accuracy of the trap-state mapping procedure. This methodology can be adopted also on other technologies, thus constituting a universal approach for the analysis of multiexponential trapping kinetics.

30 glitches in 18 radio pulsars

Pulsar timing is a classic technology of detecting irregularities in pulsar rotation. We carried out this method for 18 young radio pulsars, with long-term timing observations obtained between 2007 and 2015 using the Parkes 64-m radio telescope. As a result, 30 glitches were identified, ranging from 0.75 × 10−9 to 8.6 × 10−6 in the relative glitch sizes Δν/ν, where ν = 1/P is the pulse frequency. These glitches are composed of 26 new glitches and four published glitches with new exponential recoveries. All pulsars exhibit normal glitches, and six pulsars were observed to undergo a glitch event for the first time. We discuss the properties and implications for neutron-star physics of these glitches, and show that they are in agreement with previous work, except that the cumulative probability distributions of the mean waiting times for PSRs J0537–6910, J1341–6220 and J1740–3015 are not in consonance with the Poisson model.

Context Sensitivity across Multiple Time scales with a Flexible Frequency Bandwidth.

Everyday auditory streams are complex, including spectro-temporal content that varies at multiple timescales. Using EEG, we investigated the sensitivity of human auditory cortex to the content of past stimulation in unattended sequences of equiprobable tones. In 3 experiments including 82 participants overall, we found that neural responses measured at different latencies after stimulus onset were sensitive to frequency intervals computed over distinct timescales. Importantly, early responses were sensitive to a longer history of stimulation than later responses. To account for these results, we tested a model consisting of neural populations with frequency-specific but broad tuning that undergo adaptation with exponential recovery. We found that the coexistence of neural populations with distinct recovery rates can explain our results. Furthermore, the adaptation bandwidth of these populations depended on spectral context-it was wider when the stimulation sequence had a wider frequency range. Our results provide electrophysiological evidence as well as a possible mechanistic explanation for dynamic and multiscale context-dependent auditory processing in the human cortex.

Microgrid small‐signal stability analysis considering dynamic load model

Microgrids suitable operation depends on the system's proper design, based on accurate component models. A complete model considering entire system dynamics is a vital necessity for a successful design. Using dynamic load in microgrid small-signal model results in a model that shows transient and steady-state dynamics, since designing a low-inertia system like microgrid need extra accuracy. In this paper, an inverter-based microgrid's small-signal model in islanded operation mode containing a dynamic load model has been achieved. The Exponential Recovery Load (ERL) model is presented here to study the dynamic behavior of load. Microgrid stability analysis has been carried out for both static and dynamic load models. To attain this goal, the entire component equations are obtained and linearized around an operating point, then the state-space model is formed and eigenvalues are derived. System stability condition has been investigated by plotting eigenvalues and root locus method. In the final step, a simulation on Matlab/Simulink is performed to show the microgrids operation in the presence of a static and dynamic load.

Imperacalcin‐Induced Reduction of Sarcoplasmic Reticulum Ca 2+ in Intact Mouse Heart

Introduction Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited cardiac channelopathy, that often leads to sudden death due to arrhythmogenic episodes triggered by adrenergic stimulation. Previous studies have shown that CPVT is associated with mutations in the Ca2+ release channel of the sarcoplasmic reticulum (SR), the ryanodine receptor type-2 (RyR2). Loss of function mutations in the RyR2 result in abnormally low Ca2+ release which leads to an increase in SR Ca2+ content. It has been proposed that SR Ca2+ overload precipitates CPVT events by over activating the Na-Ca exchanger (NCX) which favors the development of arrhythmogenic delayed afterdepolarizations (DADs). Previous studies from our group and others have shown that the scorpion-derived peptide, imperacalcin (IpCa) is an effective agent to prevent/revert DADs in CPVT mouse models. The overall goal of this study was to test the hypothesis that the IpCa protects against CPVT by partially reducing SR Ca2+ content, therefore preventing the development of Ca2+ overload. To test this hypothesis, IpCa effect on SR Ca2+ content was evaluated by measuring SR Ca2+ restitution, which is the time-dependent recovery of SR Ca2+ release as a function of the stimulation frequency. If indeed, IpCa reduces SR Ca2+ content due to RyR2-mediated Ca2+ leak, SR Ca2+ restitution would be significantly shorter than in its absence. As a positive control, a known RyR2 agonist like caffeine, was used to define the effects of reducing SR Ca2+ content on SR Ca2+ restitution. Methods To test IpCa effects on SR Ca2+ restitution the pulsed local field fluorescence microscopy was used. Rhod-2AM-loaded hearts were perfused with either Tyrode, caffeine (1 mM), or IpCa (1 µM) and were stimulated at 2, 3, 4, 5, 6, 7, and 8 Hz while action potentials and intracellular Ca2+ transients were simultaneously recorded. SR Ca2+restitution was calculated from the ratio of the Ca2+ transient amplitude before and after the premature stimulation at the tested frequencies. Results At a constant stimulation frequency of 2 Hz, IpCa (1 µM; n=8) induced a 36% reduction of the Ca2+ transients amplitude, without affecting their kinetics or basal Ca2+. In contrast, caffeine (1 mM; n=10) affected basal Ca2+ (~3-fold increase), Ca2+ transients amplitude (~50% reduction), and their kinetics (~65% longer rise time & ~70% shorter decay & half-duration). As a function of the stimulation frequency, the SR Ca2+ exponential recovery (control t = 206±5 ms; n=6) was slightly accelerated by IpCa (t = 198±3 ms; n=4), & by caffeine (t = 183±4 ms; n=6). Conclusion Our results indicate that in intact mouse heart, the effects of IpCa on the intracellular Ca2+ dynamics are similar to those induced by caffeine in terms of reduction of SR Ca2+ content, without affecting the Ca2+ transient kinetics. Consistent with previous observations, our SR Ca2+ restitution results support the notion that IpCa partially depletes SR Ca2+ content, providing a plausible mechanism for its antiarrhythmic effects.

Toward Using Seismic Interferometry to Quantify Landscape Mechanical Variations after Earthquakes

ABSTRACT In mountainous terrain, large earthquakes often cause widespread coseismic landsliding as well as hydrological and hydrogeological disturbances. A subsequent transient phase with high landslide rates has also been reported for several earthquakes. Separately, subsurface seismic velocities are frequently observed to drop coseismically and subsequently recover. Consistent with various laboratory work, we hypothesize that the seismic-velocity changes track coseismic damage and progressive recovery of landscape substrate, which modulate landslide hazard and hydrogeological processes, on timescales of months to years. To test this, we analyze the near-surface seismic-velocity variations, obtained with single-station high-frequency (0.5–4 Hz) passive image interferometry, in the epicentral zones of four shallow earthquakes, for which constraints on landslide susceptibility through time exist. In the case of the 1999 Chi-Chi earthquake, detailed landslide mapping allows us to accurately constrain an exponential recovery of landslide susceptibility with a relaxation timescale of about 1 yr, similar to the pattern of recovery of seismic velocities. The 2004 Niigata, 2008 Iwate, and 2015 Gorkha earthquakes have less-resolved constraints on landsliding, but, assuming an exponential recovery, we also find matching relaxation timescales, from ∼0.1 to ∼0.6 yr, for the landslide and seismic recoveries. These observations support our hypothesis and suggest that systematic monitoring of seismic velocities after large earthquakes may help constrain and manage the evolution of landslide hazard in epicentral areas. To achieve this goal, we end by discussing several ways to improve the link between seismic velocity and landscape mechanical properties, specifically by better constraining time-dependent near-surface strength and hydrogeological changes. Hillslopes displaying coseismic surface fissuring and displacement may be an important target for future geotechnical analysis and coupled to passive geophysical investigations.

A Dynamic Active Distribution Network Equivalent for Enhancing the Generalization Capability of the Exponential Recovery Model in Stability Studies

This letter introduces an enhancement of the exponential recovery model (ERM) in order to widen its applicability and generalization capability from purely load-composed distribution networks to active distribution networks (ADNs), while maintaining its nonlinear characteristics. Although recent approaches proposed modifications of the ERM to tackle its limitation to capture bidirectional power flows, these may fail to generalize to new test scenarios with significant distributed generation (DG) due to their direct dependence on the measured power at the point of common coupling. In ADNs, this value does not represent the actual power demand of the loads. To address this issue, a new methodology based on nonlinear functions and the actual change of the signals is presented. The efficacy of the proposed model to capture the general ADN dynamics is validated using field measurements acquired over one year.

Empirical tornado resilience model for light-framed wood residential buildings

An empirical tornado resilience model based on structural functionality, a metric with clearly defined physical states, is developed for light-framed wood residential buildings using field observations of damage and recovery following the February 2017 tornado in Naplate, IL. The resilience model is composed of independent damage and recovery models that serve as a complete resilience model for residential buildings measured with the metric of structural functionality. Structural functionality is the most basic function of a building, the ability to safely provide shelter, and includes both the structural system and the building envelope. This model may be integrated into external resilience models that include measurements of other functionality components, such as lifeline services and building services, to construct a model of total functionality that includes all functionality components necessary for occupancy. The empirical tornado resilience model for light-framed wood residential buildings is an observation-based resilience model for residential buildings subject to tornado damage. It addresses the overlapping critical research needs for studies of tornado hazard, studies of residential resilience, and studies that provide a basis for validation, without replicating the existing body of resilience analysis frameworks. The included analysis using the indicators of structural functionality for wind-damaged structures reveals that some buildings trend toward zero functionality (demolition) during community-level recovery and that clear differences exist in the recovery behavior of buildings with similar post-storm structural functionality. Exponential structural functionality recovery functions are found to be appropriate for most levels of damage. Heavily damaged buildings are observed to follow a normal/s-shaped recovery.

Enzyme digestion of biofiber from mechanical heat treated municipal solid waste: Accessing kinetic and rheological design data using a pilot-scale high-solids mixer

Mechanical heat treatment of municipal solid waste offers a route for the production and separation of a biofiber fraction with high organic content, which is a potential source of sugars for biochemical conversion to chemicals and fuels. This paper describes a study of the enzymatic digestion of this biofiber fraction using a 50L commercial vertical mixer, applying a commercial cellulase. Power measurements, with calibration of mixer constants using standard Newtonian and non-Newtonian fluids were used to determine apparent viscosity of biofiber mixtures, effective shear rate and Reynolds and Power Numbers. Measurements could be easily carried out at high solids contents, >25% dry weight, where initial biofiber mixtures had high viscosity, typically 100–150 Pa S, with strong shear thinning behavior. Microscopy showed that the biofiber contained many individual wood and other plant fibers, which would entangle and so resist shear forces. Partial alignment of these fibers would be responsible for the shear-thinning effect. The fibers were repeatedly cut and reduced in length as a result of enzymatic hydrolysis, responsible for the large fall in viscosity during digestion. The viscosity of the biofiber slurries were monitored up to 48 h digestion time, with analysis of samples to determine sugar monomer content. Digestion kinetics were analyzed using an exponential recovery model, where glucose yields of around 35% were found for digestion of a biofiber derived from standard and also high paper MSW mixtures. Further yield optimization would be required to achieve commercial viability.