High-amplitude Events Research Articles

Acoustic and thermal response characteristics and failure mode of gas-bearing coal–rock composite structure under loading

Exploring the characteristics of the instability and failure processes of gas-bearing coal and rock is crucial for monitoring and predicting mine gas accidents. Thus, a real gas environment was simulated based on a self-developed gas–solid coupling infrared observation system. The acoustic–thermal response characteristics and failure mode of the gas-bearing coal–rock composite structure were studied. The results showed the following: (1) From the plastic stage, the average infrared radiation temperature of the coal increased significantly. The variances of differential infrared temperature (VDIRT) of the combination and coal started to mutate approximately 30 s before the peak, and the b value of the combination began to fluctuate frequently, while the VDIRT of rock remained approximately 2.128 × 10−4 throughout the process. (2) When stress was about to peak, a clear temperature boundary formed between coal and rock. Acoustic emissions with high energy were mainly concentrated at the interface and inside the coal. (3) The early plastic stage was dominated by high-frequency, low-amplitude events. In the post-peak stage and late plastic stage, the proportion of events with 80–90 dB amplitude rose, and there was a significant increase in low-frequency, high-amplitude events. (4) As the loading proceeded, the density and area gradually increased and tended to move toward the shear crack region. The distribution range of the rise time/amplitude expanded from 0–12 ms/V at the beginning of the loading to the range of 0–60 ms/V in the post-peak stage.

The mitochondrial calcium uniporter inhibitor Ru265 increases neuronal excitability and reduces neurotransmission via off-target effects.

Excitotoxicity due to mitochondrial calcium (Ca2+) overloading can trigger neuronal cell death in a variety of pathologies. Inhibiting the mitochondrial calcium uniporter (MCU) has been proposed as a therapeutic avenue to prevent calcium overloading. Ru265 (ClRu(NH3)4(μ-N)Ru(NH3)4Cl]Cl3) is a cell-permeable inhibitor of the mitochondrial calcium uniporter (MCU) with nanomolar affinity. Ru265 reduces sensorimotor deficits and neuronal death in models of ischemic stroke. However, the therapeutic use of Ru265 is limited by the induction of seizure-like behaviours. We examined the effect of Ru265 on synaptic and neuronal function in acute brain slices and hippocampal neuron cultures derived from mice, in control and where MCU expression was genetically abrogated. Ru265 decreased evoked responses from calyx terminals and induced spontaneous action potential firing of both the terminal and postsynaptic principal cell. Recordings of presynaptic Ca2+ currents suggested that Ru265 blocks the P/Q type channel, confirmed by the inhibition of currents in cells exogenously expressing the P/Q type channel. Measurements of presynaptic K+ currents further revealed that Ru265 blocked a KCNQ current, leading to increased membrane excitability, underlying spontaneous spiking. Ca2+ imaging of hippocampal neurons showed that Ru265 increased synchronized, high-amplitude events, recapitulating seizure-like activity seen in vivo. Importantly, MCU ablation did not suppress Ru265-induced increases in neuronal activity and seizures. Our findings provide a mechanistic explanation for the pro-convulsant effects of Ru265 and suggest counter screening assays based on the measurement of P/Q and KCNQ channel currents to identify safe MCU inhibitors.

Time-varying damage evolution of concrete under cyclic disturbance loading- an experimental observation utilizing AE and DIC

Cyclic disturbance loading affects the continuous operation of concrete structures. This study aims to better understand the failure behavior of concrete structures under cyclic disturbance loading. This study combined acoustic emission (AE) and digital image correlation (DIC) technologies to study mechanical failure behavior and damage evolution of concrete materials under cyclic disturbance loading and unloading. The AE event time-frequency characteristics, surface principal strain program, and damage parameters of samples with different cyclic disturbance amplitudes were obtained by theoretical calculation. The results reveal that when minor disturbance amplitudes are applied, the elastic modulus of concrete specimens tends to increase. When the disturbance amplitude is too large, the elastic modulus of the specimens drops, leading to faster specimen failure. The AE characteristic parameters exhibit a Felicity effect after the sample is subjected to a cyclic disturbance loading. Moreover, the larger the amplitude of the disturbance load, the more frequent the low-frequency and high-amplitude events generated during the final rupture, the higher the concentration of the principal strain on the sample's surface, and the wider the crack band distribution. AE energy and Effective crack are consistent in characterizing damage, and the changing trend of these two damage parameters can better reflect the deterioration process of concrete. The research results will provide practical and theoretical insights for safely operating and maintaining concrete structures.

Acoustics Reveals Short‐Term Air Temperature Fluctuations Near Mars' Surface

AbstractAcoustics is new on Mars: it allows the characterization of turbulence at smaller scales than previously possible within the lowest part of the Planetary Boundary Layer. Sound speed measurements, by the SuperCam instrument and its microphone onboard the NASA Perseverance rover, allow the retrieval of atmospheric temperatures at 0.77 m above the ground, at 3 Hz, with a ∼10 ms response time that is 20–100 times shorter than for typical thermocouple sensors used on Mars. Here we report on the first measurements of the sound speed‐derived temperature and its fluctuations near the surface. Data highlight large and rapid fluctuations up to ±7 K/s, whose amplitude over such a timescale has never been reported, nor predicted by atmospheric models. These fluctuations follow the daytime pattern of the turbulence and highlight occasional high amplitude events that are likely due to the conjunction of low thermal inertia and strong winds.

Damage characteristics and constitutive model of concrete under uniaxial compression after Freeze-Thaw damage

In order to study the uniaxial compressive damage characteristics and stress–strain behavior of concrete with different degrees of freeze–thaw (F-T) damage, and then effectively evaluate the mechanical properties of concrete under different F-T damage degree. The rapid F–T cycle test was performed on different groups of concrete specimens, and an F–T damage evolution equation was established according to the change law of the relative dynamic elastic modulus. Uniaxial compression tests were performed on specimens with different F–T cycles, and damage evolution during compression was studied using an acoustic emission (AE) system. Finally, the AE characteristic parameters were used to establish a uniaxial compression constitutive model of concrete considering F–T damage. The results showed that the degree of F–T damage increased as the F–T cycles increased. During the concrete compression failure, the AE amplitude showed a more obvious and rapid rising trend when it was close to the critical state point. The proportion of low-amplitude AE events (≤50 dB) gradually decreased, whereas that of medium- and high-amplitude events exhibited a corresponding upward trend. These results indicate that the concrete after F–T damage exhibited more brittle characteristics during the compression failure process. The damage constitutive model established in this study can accurately reflect the damage evolution law of concrete during the entire process of uniaxial compression after F–T cycles. Moreover, the model was sufficiently consistent with test data, providing a reference for the design and safe operation of concrete structures in cold regions.

Extreme vorticity events in turbulent Rayleigh-Bénard convection from stereoscopic measurements and reservoir computing

High-amplitude events of the out-of-plane vorticity component ${\ensuremath{\omega}}_{z}$ are analyzed by stereoscopic particle image velocimetry (PIV) in the bulk region of turbulent Rayleigh-B\'enard convection in air. The Rayleigh numbers $\mathrm{Ra}$ vary from $1.7\ifmmode\times\else\texttimes\fi{}{10}^{4}$ to $5.1\ifmmode\times\else\texttimes\fi{}{10}^{5}$. The experimental investigation is connected with a comprehensive statistical analysis of long-term time series of ${\ensuremath{\omega}}_{z}$ and individual velocity derivatives $\ensuremath{\partial}{u}_{i}/\ensuremath{\partial}{x}_{j}$. A statistical convergence for derivative moments up to an order of 6 is demonstrated. Our results are found to agree well with existing high-resolution direct numerical simulation data in the same range of parameters, including the extreme vorticity events that appear in the far exponential tails of the corresponding probability density functions. The transition from Gaussian to non-Gaussian velocity derivative statistics in the bulk of a convection flow is confirmed experimentally. The experimental data are used to train a reservoir computing model, one implementation of a recurrent neural network, to reproduce highly intermittent experimental time series of the vorticity and thus reconstruct extreme out-of-plane vorticity events. After training the model with high-resolution PIV data, the machine learning model is run with sparsely seeded, continually available, and unseen measurement data in the reconstruction phase. The dependence of the reconstruction quality on the sparsity of the partial observations is also documented. Our latter result paves the way to machine-learning-assisted experimental analyses of small-scale turbulence for which time series of missing velocity derivatives can be provided by generative algorithms.

Moisture origin, transport pathways, and driving processes of intense wintertime moisture transport into the Arctic

Abstract. A substantial portion of the moisture transport into the Arctic occurs in episodic, high-amplitude events with strong impacts on the Arctic's climate system components such as sea ice. This study focuses on the origin of such moist-air intrusions during winter and examines the moisture sources, moisture transport pathways, and their linkage to the driving large-scale circulation patterns. For that purpose, 597 moist-air intrusions, defined as daily events of intense (exceeding the 90th anomaly percentile) zonal mean moisture transport into the polar cap (≥70∘ N), are identified. Kinematic backward trajectories combined with a Lagrangian moisture source diagnostic are then used to pinpoint the moisture sources and characterize the airstreams accomplishing the transport. The moisture source analyses show that the bulk of the moisture transported into the polar cap during these moist-air intrusions originates in the eastern North Atlantic with an uptake maximum poleward of 50∘ N. Trajectories further reveal an inverse relationship between moisture uptake latitude and the level at which moisture is injected into the polar cap, consistent with ascent of poleward-flowing air in a baroclinic atmosphere. Focusing on intrusions in the North Atlantic (424 intrusions), we find that lower tropospheric moisture transport is predominantly accomplished by two types of airstreams: (i) cold, polar air warmed and moistened by surface fluxes and (ii) air subsiding from the mid-troposphere into the boundary layer. Both airstreams contribute about 36 % each to the total transport. The former accounts for most of the moisture transport during intrusions associated with an anomalously high frequency of cyclones east of Greenland (218 intrusions), whereas the latter is more important in the presence of atmospheric blocking over Scandinavia and the Ural Mountains (145 events). Long-range moisture transport, accounting for 17 % of the total transport, dominates during intrusions with weak forcing by baroclinic weather systems (64 intrusions). Finally, mid-tropospheric moisture transport is invariably associated with (diabatically) ascending air and moisture origin in the central and western North Atlantic, including the Gulf Stream front, accounting for roughly 10 % of the total transport. In summary, our study shows that moist-air intrusions into the polar atmosphere result from a combination of airstreams with predominantly high-latitude or high-altitude origin, whose relative importance is determined by the underlying driving weather systems (i.e., cyclones and blocks).

Rhythmicity in heart rate and its surges usher a special period of sleep, a likely home for PGO waves.

High amplitude electroencephalogram (EEG) events, like unitary K-complex (KC), are used to partition sleep into stages and hence define the hypnogram, a key instrument of sleep medicine. Throughout sleep the heart rate (HR) changes, often as a steady HR increase leading to a peak, what is known as a heart rate surge (HRS). The hypnogram is often unavailable when most needed, when sleep is disturbed and the graphoelements lose their identity. The hypnogram is also difficult to define during normal sleep, particularly at the start of sleep and the periods that precede and follow rapid eye movement (REM) sleep. Here, we use objective quantitative criteria that group together periods that cannot be assigned to a conventional sleep stage into what we call REM0 periods, with the presence of a HRS one of their defining properties. Extended REM0 periods are characterized by highly regular sequences of HRS that generate an infra-low oscillation around 0.05 Hz. During these regular sequence of HRS, and just before each HRS event, we find avalanches of high amplitude events for each one of the mass electrophysiological signals, i.e. related to eye movement, the motor system and the general neural activity. The most prominent features of long REM0 periods are sequences of three to five KCs which we label multiple K-complexes (KCm). Regarding HRS, a clear dissociation is demonstrated between the presence or absence of high gamma band spectral power (55–95 Hz) of the two types of KCm events: KCm events with strong high frequencies (KCmWSHF) cluster just before the peak of HRS, while KCm between HRS show no increase in high gamma band (KCmNOHF). Tomographic estimates of activity from magnetoencephalography (MEG) in pre-KC periods (single and multiple) showed common increases in the cholinergic Nucleus Basalis of Meynert in the alpha band. The direct contrast of KCmWSHF with KCmNOHF showed increases in all subjects in the high sigma band in the base of the pons and in three subjects in both the delta and high gamma bands in the medial Pontine Reticular Formation (mPRF), the putative Long Lead Initial pulse (LLIP) for Ponto-Geniculo-Occipital (PGO) waves.

Experimental investigation on stability and early warning of waste dump using guided wave monitoring

Waste dump landslides caused by the excavation of the base of the waste dump slope were simulated, and the guided wave technique was applied for waste dump stability monitoring. The influence of inner diameter and wall thickness of waveguides on guided wave attenuation is analyzed. The variation characteristics of the ring down count (RDC) rate and the trend of b value during landslide are discussed, which provides a theoretical basis for the guided wave monitoring and early warning for the stability of waste dumps. The results show that: (1) The guided wave signal attenuation is related to the frequency and the wall thickness, while the inner diameter has little effect. In the range of 0∼170 kHz, the signal attenuation increases with the frequency. In the range of 170∼512 kHz, the higher the frequency and the thicker the wall, the greater the signal attenuation is. (2) Guided wave RDC rate and video monitoring can reflect the whole process of landslide. The RDC rate curves have three prominent data peaks, which implies three landslide accidents. The video monitoring can respond to the whole process of changes in the scene in real-time. The change of parameter curve is more intuitive than the field picture. (3) The b value fluctuates significantly during the instability of the waste dump. At the early stage of the waste dump landslide, low-amplitude guided wave events are the majority, and the b value is at a high level. When a landslide occurs, the high amplitude events caused by friction and collision between gravel and waveguide increase rapidly, and the b value drops to the minimum value rapidly. When the waste dump is readjusted to the equilibrium state, the b value shows an upward trend. There is an obvious turning point in the b value curve before waste dump failure, which can be used as the precursor of landslide.

Acceptability of the effective strain damage model for fatigue life assessment considering the load sequence effect for automotive coil spring

This paper aims to assess the effective strain damage (ESD) model with a durability analysis of an automobile coil spring under consideration of the load sequence effect. Conventional strain-life models such as Coffin-Manson, Morrow and Smith-Watson-Topper are insufficient in predicting fatigue life under the consideration of the load sequence effect. Strain time histories of coil springs were captured based on three types of road conditions: highway, campus and industrial roads. In order to determine the fatigue life, the ESD and conventional strain-life models were employed. The strain-life models predicted lower fatigue life values for campus and industrial roads, which contained many high amplitude events. Similar fatigue life predictions for ESD and conventional strain-life models were found on the highway due to the absence of high amplitude events, which led to a minimal load sequence effect. The suitability of the ESD model was verified through the Weibull probability plot, in which the ESD model fitted well to the distribution compared to conventional strain-life models. The main contribution is that load interactions have a significant influence on predicting fatigue life within the random strain histories of the fatigue properties of a coil spring.

Observing Earth\u2019s magnetic environment with the GRACE-FO mission

The Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission carries magnetometers that are dedicated to enhance the satellite’s navigation. After appropriate calibration and characterisation of artificial magnetic disturbances, these observations are valuable assets to characterise the natural variability of Earth’s magnetic field. We describe the data pre-processing, the calibration, and characterisation strategy against a high-precision magnetic field model applied to the GRACE-FO magnetic data. During times of geomagnetic quiet conditions, the mean residual to the magnetic model is around 1 nT with standard deviations below 10 nT. The mean difference to data of ESA’s Swarm mission, which is dedicated to monitor the Earth’s magnetic field, is mainly within ± 10 nT during conjunctions. The performance of GRACE-FO magnetic data is further discussed on selected scientific examples. During a magnetic storm event in August 2018, GRACE-FO reveals the local time dependence of the magnetospheric ring current signature, which is in good agreement with results from a network of ground magnetic observations. Also, derived field-aligned currents (FACs) are applied to monitor auroral FACs that compare well in amplitude and statistical behaviour for local time, hemisphere, and solar wind conditions to approved earlier findings from other missions including Swarm. On a case event, it is demonstrated that the dual-satellite constellation of GRACE-FO is most suitable to derive the persistence of auroral FACs with scale lengths of 180 km or longer. Due to a relatively larger noise level compared to dedicated magnetic missions, GRACE-FO is especially suitable for high-amplitude event studies. However, GRACE-FO is also sensitive to ionospheric signatures even below the noise level within statistical approaches. The combination with data of dedicated magnetic field missions and other missions carrying non-dedicated magnetometers greatly enhances related scientific perspectives.

Spatiotemporal Patterns of High-Frequency Activity (80-170 Hz) in Long-Term Intracranial EEG.

To determine the utility of high-frequency activity (HFA) and epileptiform spikes as biomarkers for epilepsy, we examined the variability in their rates and locations using long-term ambulatory intracranial EEG (iEEG) recordings. This study used continuous iEEG recordings obtained over an average of 1.4 years from 15 patients with drug-resistant focal epilepsy. HFA was defined as 80- to 170-Hz events with amplitudes clearly larger than the background, which was automatically detected with a custom algorithm. The automatically detected HFA was compared with visually annotated high-frequency oscillations (HFOs). The variations of HFA rates were compared with spikes and seizures on patient-specific and electrode-specific bases. HFA included manually annotated HFOs and high-amplitude events occurring in the 80- to 170-Hz range without observable oscillatory behavior. HFA and spike rates had high amounts of intrapatient and interpatient variability. Rates of HFA and spikes had large variability after electrode implantation in most of the patients. Locations of HFA and spikes varied up to weeks in more than one-third of the patients. Both HFA and spike rates showed strong circadian rhythms in all patients, and some also showed multiday cycles. Furthermore, the circadian patterns of HFA and spike rates had patient-specific correlations with seizures, which tended to vary across electrodes. Analysis of HFA and epileptiform spikes should consider postimplantation variability. HFA and epileptiform spikes, like seizures, show circadian rhythms. However, the circadian profiles can vary spatially within patients, and their correlations to seizures are patient-specific.

Vortex merging events during amplitude switching in mixed-mode pressure oscillations in a partially premixed backward facing combustor

The role of hydrodynamics resulting in the mixed-mode oscillations (MMO) of unsteady pressure in a backward facing step combustor with partially premixed flame is investigated using time-resolved particle image velocimetry and CH* chemiluminescence imaging. This mode of pressure oscillations comprises switching between high-amplitude oscillations dictated by acoustic mode and/vortex mode and low-amplitude oscillations. The high-amplitude oscillations are marked by intense flow and flame modulation, while the low-amplitude oscillations are accompanied by small-scale structures on the shear layer, that are sedate in driving the heat release oscillations. The small-scales override on the elongated flame that resides in the recirculation zone of the step. The key aspect of the present work is in identifying the transitional events that result in the decay/ onset of high-amplitudes. This is achieved by tracking vortex cores at each instant during the transition. The small-scale shear layer structures, that are present during low-amplitude events merge as they convect with the flow. The identified vortex cores on the shear layer and in the recirculation zone reduce in their multiplicity as the merger progresses. This subsequently results in the genesis of a large-scale structure that modulates the flame coherently, thereby triggering high-amplitude oscillations. This is corroborated with identifying the presence of a single vortex core resulting in high amplitude events.

Near‐Coastal Winter Waves From Microseisms

AbstractLong‐term coastal wave climate variability cannot be reliably assessed from relatively short duration buoy observations that began about 1980. Microseisms at double the wave frequency (DFM) provide a proxy record of coastal wave activity. Here, we show that winter (November to March) wave activity can be well characterized from near‐coastal seismometer DFM observations, although extreme wave events are not consistently well reproduced. Reconstructed mean winter seismic significant wave height, sHs, determined using simultaneous seismic and buoy observations, closely track nearby buoy Hs over 1992–2017 winters. Buoy‐measured mean winter short‐period wave variability in the [0.1, 0.15] Hz band is also well reproduced. Generally lower sHs for high amplitude events, compared with offshore buoy Hs, suggests that DFM generation is closer to the coast where shore‐reflected long‐period opposing wave components are likely higher. These results indicate that digitized pre‐1980 archived analog seismograms at near‐coastal seismic stations can reliably characterize long‐term wave climate changes and decadal variability.

Past perspectives on the present era of abrupt Arctic climate change

Abrupt climate change is a striking feature of many climate records, particularly the warming events in Greenland ice cores. These abrupt and high-amplitude events were tightly coupled to rapid sea-ice retreat in the North Atlantic and Nordic Seas, and observational evidence shows they had global repercussions. In the present-day Arctic, sea-ice loss is also key to ongoing warming. This Perspective uses observations and climate models to place contemporary Arctic change into the context of past abrupt Greenland warmings. We find that warming rates similar to or higher than modern trends have only occurred during past abrupt glacial episodes. We argue that the Arctic is currently experiencing an abrupt climate change event, and that climate models underestimate this ongoing warming. In recent decades, the Arctic has warmed at over twice the global rate. This Perspective places these trends into the context of abrupt Dansgaard–Oeschger warming events in the palaeoclimate record, arguing that the contemporary Arctic is undergoing comparably abrupt climate change.

Trends in northern midlatitude atmospheric wave power from 1950 to 2099

In a warming climate, atmospheric wave activity and associated weather patterns may change, although conflicting results have been reported on this topic. Additionally, atmospheric wave changes in a future climate have mainly focused on waves of a specified spatial scale, rather than a particular spatiotemporal scale. Here, changes in the variability of Rossby waves of multiple spatiotemporal scales are analyzed using the wavenumber-frequency power spectrum, a tool commonly applied to analyze atmospheric equatorial waves. Daily 500 hPa geopotential height data over 40°–60°N from historical (1950–2005) and future (2006–2099) simulations from 20 models in the Coupled Model Intercomparison Project Phase 5 (CMIP5) under the RCP8.5 scenario were analyzed. When compared to the historical period, the late 21st century climate projections showed a decline in spectral power for both eastward and westward propagating waves with wavenumbers greater than 8 that spanned over all frequencies in all seasons, but an increase in mean power for eastward propagating waves with wavenumbers 1–7 over all frequencies was shown in winter and spring. This increase in power was accompanied by increased variance, i.e., an increased meridional extent of 500 hPa ridges and troughs, and was the result of increases in the mean number of high amplitude events and duration of activity within this wave band. These results indicate that large-scale (~ 104 km) eastward propagating weather systems may intensify with higher amplitudes for ridges and troughs, while short-scale (102–103 km) weather systems may decrease in their intensity due to reduced variability in the late 21st century under the high emissions scenario. Potential mechanisms for these changes are discussed, including enhanced Arctic warming and midlatitude-tropical interactions.

Application of Seismic Attribute and Spectral Decomposition: Example of Fluvial System During Miocene in Field A, Malay Basin

Stratigraphic channels in field A Malay Basin including those with reservoir potential have been defined seismically. There were two exploration wells in field a however, the wells were abandoned due to low structural relief and volume were below economic criteria. This study discusses how seismic attribute and spectral decomposition give geomorphological information in different stratigraphic levels of Miocene age at Top F, H, I, Group I-50 and I-60. Facies analysis, seismic attribute, spectral decomposition and colour blending were implemented to identify hydrocarbon potential in stratigraphic traps and to enhance seismic resolution. Channel anomalies can be identified in seismic reflections characterized by high-amplitude events with chaotic reflections. Numerous sub-parallel reflection with high amplitude is observed in the upper formation. Several seismic attributes were used from the 3D seismic dataset to identify the geomorphologic features, potential reservoir variations, besides distribution and to extract the anomalies. Physical attributes which are related to amplitude, frequency, phase and their derivative were used including variance, instantaneous frequency, sweetness and spectral decomposition. Sweetness is the combination of lateral continuity and reflection strength. High reflection strength indicates maximum amplitude of the largest peak or through of real trace. This is especially, true when an event is a composite reflection. Amplitude attribute provides better spatial definition of events and bright spots could be enhanced. Instantaneous frequency shows composite frequency of the individual reflections contributing to a particular reflector. This composite is a useful correlation tool. Rapid changes in frequency are sometimes indicator of pinchouts such as oil/gas and water contacts. Low frequency anomalies are observed in zones below hydrocarbon reservoirs. Meanwhile, instantaneous phase is useful in stratigraphic analysis of certain sections because the sharp zero crossings that results may emphasize lateral discontinuities, pinchouts and angularities. The combination of attribute analysis and spectral decomposition aids the interpretation and identification of some channel patterns and channel distribution. Two methods of spectral decomposition are used Short Time Fourier Transform (STFT) and S-transform which focus on spatial and temporal range, respectively. Red Green Blue (RGB) colour blending represents different frequency ranges of low, mid and high frequency bands and display as a single image. This method reveals additional information such as depositional elements, anomaly identification, bed thickness, presence of fluids and help to resolve petrophysical heterogeneity. This study reveals that there are strong evidences of hydrocarbon potential in stratigraphic traps for further exploration within the study area. © Medwell Journals, 2019.

Dissecting beta-state changes during timed movement preparation in Parkinson’s disease

An emerging perspective describes beta-band (15−28 Hz) activity as consisting of short-lived high-amplitude events that only appear sustained in conventional measures of trial-average power. This has important implications for characterising abnormalities observed in beta-band activity in disorders like Parkinson’s disease. Measuring parameters associated with beta-event dynamics may yield more sensitive measures, provide more selective diagnostic neural markers, and provide greater mechanistic insight into the breakdown of brain dynamics in this disease. Here, we used magnetoencephalography in eighteen Parkinson’s disease participants off dopaminergic medication and eighteen healthy control participants to investigate beta-event dynamics during timed movement preparation. We used the Hidden Markov Model to classify event dynamics in a data-driven manner and derived three parameters of beta events: (1) beta-state amplitude, (2) beta-state lifetime, and (3) beta-state interval time. Of these, changes in beta-state interval time explained the overall decreases in beta power during timed movement preparation and uniquely captured the impairment in such preparation in patients with Parkinson’s disease. Thus, the increased granularity of the Hidden Markov Model analysis (compared with conventional analysis of power) provides increased sensitivity and suggests a possible reason for impairments of timed movement preparation in Parkinson’s disease.

High-precision seismic data reconstruction with multi-domain sparsity constraints based on curvelet and high-resolution Radon transforms

In recent years, the sparsity-promoting reconstruction method based on the compressed sensing theory has been rapidly developed and applied to seismic data reconstruction. Many achievements have been made toward providing high-quality reconstruction by using undersampled data. However, the problem of insufficient reconstruction in null traces still hinders us a lot in practical applications, especially for complex seismic data. Aiming to solve this problem, we made full use of the sparsity characteristics of seismic data in multiple sparse transform domains and jointly reconstructed seismic data to realize the complementary advantages of multiple sparse transforms; As such, we propose a high-precision seismic data recovery method with multi-domain sparsity constraints based on curvelet and high-resolution Radon transforms. Numerical examples by synthetic and real data showed that the new approach can achieve a better reconstruction result than the commonly used curvelet-based recovery method. Integrated with the curvelet transform to develop new recovery method, the high-resolution Radon transform has more advantages than the conventional Radon transform for overcoming the shortcomings associated with the insufficient reconstruction of high-amplitude events. At the same time, the method is also applicable for developing new reconstruction methods by combining other sparse transforms depending on the characteristics of seismic data. The reconstruction method with multi-domain sparsity constraints can easily be extended to three-dimensional situation.

National Gas Hydrate Program expedition 02: Identification of gas hydrate prospects in the Krishna-Godavari Basin, offshore India

After completing the first expedition of India's National Gas Hydrate Program (NGHP-01) in 2006, it was concluded that for the next expedition (National Gas Hydrate Program 02; NGHP-02), a new drill site review effort should focus on identifying potential deep-water offshore gas hydrate accumulations in sand dominated depositional environments. Therefore, geological and geophysical data analysis and 3D seismic data interpretation along with associated seismic modeling were carried out in three areas of the Krishna-Godavari Basin: Areas B, C, and E. Conventional petroleum exploration approaches of seismic amplitude evaluation were adapted to prospect for potentially sand-rich depositional systems within the gas hydrate stability zone. Subsequently, these prospective areas were further assessed through the geological and geophysical evaluation of depositional setting, gas sources, and gas migration pathways. In Area B, prospecting focused on a large anticlinal structure with a prominent bottom-simulating reflector and several key horizons that indicated evidence for potential sand-hosted hydrate occurrences. In Area C, the prospects were distributed throughout various settings within a very large deep-water channel-levee-fan system with complex indications of potential gas hydrate occurrence in sand-prone seismic facies. In Area E, prospects were associated with high amplitude events within inferred channel-levee sequences. Based on the pre-expedition/onboard drill-site evaluation, the 22 most promising sites in the Krishna-Godavari Basin were identified and prioritized to investigate and delineate a total of 17 identified gas hydrate prospects. This paper describes the geo-scientific studies carried out prior to NGHP-02 for site identification, evaluation and prioritization. An important outcome of this study is the identification of two potentially producible gas hydrate systems inferred to host significant quantities of gas hydrate in stratigraphic-structural traps.