Waveform Duration Research Articles

Analysis of spark-generated waveforms coalescing in air using schlieren imaging

Mach waves generated by turbulent structures in supersonic jet flows have the potential to intersect and coalesce, a process proposed as a significant contributor to acoustic waveform steepening in the near field of a jet and to the noise referred to as crackle [Baars et al., AIAA (2013); Fiévet et al., AIAA (2016)]. Numerical simulations of intersecting waveforms have demonstrated that coalescence can lead to increased steepening that is dependent on intersection angle, waveform duration, and geometrical spreading [Willis et al., AIAA (2022)]. In this study, two simplified experiments involving a spark source in air are examined. The first involves grazing incidence on a rigid plane to model symmetric intersection between waveforms. The second involves intersecting waveforms emanating from side-by-side openings in a 3D-printed enclosure. Measurements of nonlinear evolution were made for the intersecting waveforms produced with each experimental setup and compared with measurements made for one waveform alone. Schlieren images of the coalescing waves allow for comparison of waveform steepening between the two cases without the limitations imposed by microphones. The measurements permit assessment of the extent to which coalescence enhances waveform steepening. [WAW is supported by the ARL:UT Chester M. McKinney Graduate Fellowship in Acoustics.]

ECG segmentation algorithm based on bidirectional hidden semi-Markov model

Accurate segmentation of electrocardiogram (ECG) waves is crucial for cardiovascular diseases (CVDs). In this study, a bidirectional hidden semi-Markov model (BI-HSMM) based on the probability distributions of ECG waveform duration was proposed for ECG wave segmentation. Four feature-vectors of ECG signals were extracted as the observation sequence of the hidden Markov model (HMM), and the statistical probability distribution of each waveform duration was counted. Logistic regression (LR) was used to train model parameters. The starting and ending positions of the QRS wave were first detected, and thereafter, bidirectional prediction was employed for the other waves. Forwardly, ST segment, T wave, and TP segment were predicted. Backwardly, P wave and PQ segments were detected. The Viterbi algorithm was improved by integrating the recursive formula of the forward prediction and backward backtracking algorithms. In the QT database, the proposed method demonstrated excellent performance (Acc = 97.98%, F1 score of P wave = 98.37%, F1 score of QRS wave = 97.60%, F1 score of T wave = 97.79%). For the wearable dynamic electrocardiography (DCG) signals collected by the Shandong Provincial Hospital (SPH), the detection accuracy was 99.71% and the F1 of each waveform was above 99%. The experimental results and real DCG signal validation confirmed that the proposed new BI-HSMM method exhibits significant ability to segment the resting and DCG signals; this is conducive to the detection and monitoring of CVDs.

Error bounds for extended source inversion applied to an acoustic transmission inverse problem

A simple inverse problem for the wave equation requires determination of both the wave velocity in a homogenous acoustic material and the transient waveform of an isotropic point radiator, given the time history of the wavefield at a remote point in space. The duration (support) of the source waveform and the source-to-receiver distance are assumed known. A least squares formulation of this problem exhibits the ‘cycle-skipping’ behavior observed in field scale problems of this type, with many local minima differing greatly from the global minimizer. An extended formulation, dropping the support constraint on the source waveform in favor of a weighted quadratic penalty, eliminates this misbehaviour. With proper choice of the weight operator, the velocity component at any local minimizer of this extended objective function differs from the global minimizer of the least-squares formulation by less than a linear combination of the source waveform support radius and data noise-to-signal ratio.

Enhancing convolutional neural network predictions of electrocardiograms with left ventricular dysfunction using a novel sub-waveform representation

BackgroundElectrocardiogram (ECG) deep learning (DL) has promise to improve the outcomes of patients with cardiovascular abnormalities. In ECG DL, researchers often use convolutional neural networks (CNNs) and traditionally use the full duration of raw ECG waveforms that create redundancies in feature learning and result in inaccurate predictions with large uncertainties.ObjectiveFor enhancing these predictions, we introduced a sub-waveform representation that leverages the rhythmic pattern of ECG waveforms (data-centric approach) rather than changing the CNN architecture (model-centric approach).ResultsWe applied the proposed representation to a population with 92,446 patients to identify left ventricular dysfunction. We found that the sub-waveform representation increases the performance metrics compared to the full-waveform representation. We observed a 2% increase for area under the receiver operating characteristic curve and 10% increase for area under the precision-recall curve. We also carefully examined three reliability components of explainability, interpretability, and fairness. We provided an explanation for enhancements obtained by heartbeat alignment mechanism. By developing a new scoring system, we interpreted the clinical relevance of ECG features and showed that sub-waveform representation further pushes the scores towards clinical predictions. Finally, we showed that the new representation significantly reduces prediction uncertainties within subgroups that contributes to individual fairness.ConclusionWe expect that this added control over the granularity of ECG data will improve the DL modeling for new artificial intelligence technologies in the cardiovascular space.

Seismic Performance Assessment of Wide Pile-Supported Wharf Considering Soil Slope and Waveform Duration

Pile-supported wharf (PSW) is one of the primary port structures and is often damaged by earthquakes. To mitigate the risk of seismic damage to a PSW, its seismic performance should be thoroughly assessed. This study aimed to examine the impact of ground displacement on the seismic performance of PSW with a mild soil slope. We performed soil-structure system finite element analysis targeting a wide PSW. The analysis is divided into two scenarios. In the first scenario, the PSW was modeled without regard for the soil slope, whereas the second scenario considered the soil slope. Two waveforms that matched the target spectral acceleration were used to study the effects of the waveform duration on the seismic response of PSW. The analysis results revealed substantial influences of soil slope displacement as well as differences in waveforms on PSW’s seismic performance.

Short-Pulsed Metamaterials.

We study a class of temporal metamaterials characterized by time-varying dielectric permittivity waveforms of duration much smaller than the characteristic wave-dynamical timescale. In the analogy between spatial and temporal metamaterials, such a short-pulsed regime can be viewed as the temporal counterpart of metasurfaces. We introduce a general and compact analytical formalism for modeling the interaction of a short-pulsed metamaterial with an electromagnetic wave packet. Specifically, we elucidate the role of local and nonlocal effects, as well as the time-reversal symmetry breaking, and we show how they can be harnessed to perform elementary analog computing, such as first and second derivatives. Our theory validated against full-wave numerical simulations suggests a novel route for manipulating electromagnetic waves without relying on long, periodic temporal modulations. Just as metasurfaces have played a pivotal role in the technological viability and practical applicability of conventional (spatial) metamaterials, short-pulsed metamaterials may catalyze the development of temporal and space-time metamaterials.

Screening and Evaluation for Antixenosis Resistance in Wheat Accessions and Varieties to Grain Aphid, Sitobion miscanthi (Takahashi) (Hemiptera: Aphididae).

The grain aphid, Sitobion miscanthi causes serious damage by removing nutritional content from wheat plants and transmitting viral diseases. The use of resistant wheat cultivars is an effective method of aphid management. To identify S. miscanthi resistant cultivars, preliminary antixenosis resistance screening was conducted on 112 Ethiopian and 21 Chinese wheat accessions and varieties along with bioassay to test for further antixenosis resistance, identification of aphid feeding behavior using electrical penetration graph (EPG), and imaging of leaf trichome densities using a 3D microscope. According to antixenosis resistance screening, one highly-resistant, 25 moderately-resistant, and 38 slightly-resistant wheat cultivars to S. miscanthi were identified. Aphid choice tests showed that Luxuan266, 243726, and 213312 were the least preferred after 12, 24, 48, and 72 h of S. miscanthi release. Longer duration of Np, longer time to first probe, and shorter duration of E2 waveforms were recorded in Lunxuan266, 243726, and 213312 than in Beijing 837. The trichome density on adaxial and abaxial leaf surfaces of Lunxuan266, 243726 and 213312 was significantly higher than on those of Beijing 837. We concluded that Lunxuan266, 243726, and 213312 were antixenosis resistant to S. miscanthi based on the choice test, EPG results, and leaf trichome densities.

The role of the cardiomyocyte circadian clocks in ion channel regulation and cardiac electrophysiology.

Daily variations in cardiac electrophysiology and the incidence for different types of arrhythmias reflect ≈24h changes in the environment, behaviour and internal circadian rhythms. This article focuses on studies that use animal models to separate the impact that circadian rhythms, as well as changes in the environment and behaviour, have on 24h rhythms in heart rate and ventricular repolarization. Circadian rhythms are initiated at the cellular level by circadian clocks, transcription-translation feedback loops that cycle with a periodicity of 24h. Several studies now show that the circadian clock in cardiomyocytes regulates the expression of cardiac ion channels by multiple mechanisms; underlies time-of-day changes in sinoatrial node excitability/intrinsic heart rate; and limits the duration of the ventricular action potential waveform. However, the 24h rhythms in heart rate and ventricular repolarization are primarily driven by autonomic signalling. A functional role for the cardiomyocyte circadian clock appears to buffer the heart against perturbations. For example, the cardiomyocyte circadian clock limits QT-interval prolongation (especially at slower heart rates), and it may facilitate the realignment of the 24h rhythm in heart rate to abrupt changes in the light cycle. Additional studies show that modifying rhythmic behaviours (including feeding behaviour) can dramatically impact the 24h rhythms in heart rate and ventricular repolarization. If these mechanisms are conserved, these studies suggest that targeting endogenous circadian mechanisms in the heart, as well as modifying the timing of certain rhythmic behaviours, could emerge as therapeutic strategies to support heart function against perturbations and regulate 24h rhythms in cardiac electrophysiology.

Perceived Depth and Roughness of Virtual Buttons With Touchscreens.

With the rapidly increasing penetration of touchscreens in various application sectors, more sophisticated and configurable haptic effects can be rendered on touchscreens (e.g., buttons). In this paper, we presented a design process to instantiate a wide range of vibrotactile stimuli for rendering various virtual buttons on touchscreens. We study the perceived depth and roughness of rendered virtual buttons. There are two stages: the design of the drive signals and the main study. We generated and screened drive signals to render vibrotactile stimuli for virtual buttons through varying envelope shapes, superposition methods, compound waveform composition (CWC) types, durations, and frequencies. The results show that the perceived depth of virtual buttons can be very deep, and the perceived roughness can be very rough around the resonant frequency. Perceived depth and roughness decrease when the frequency increases or decreases from the resonant frequency. A longer duration of vibrotactile stimuli and adding pulse numbers could increase the perceived depth and roughness. Perceived depth and roughness have a similar trend with varying frequencies at a fixed duration.

Open-source low-cost cardiac optical mapping system.

Fluorescent imaging with voltage- or calcium-sensitive dyes, known as optical mapping, is one of the indispensable modern techniques to study cardiac or neural electrophysiology, unsurpassed by temporal and spatial resolution. High-speed CMOS cameras capable of optical registration of action potential propagation are in general very costly. We present a complete solution priced below US$1,000 (including camera and lens) at the moment of publication with an open-source image acquisition and processing software. We demonstrate that the iDS UI-3130CP rev.2 camera we used in this study is capable of 200x200 977 frames per second (FPS) action potential recordings from rodent hearts, with the signal-to-noise-ratio of a conditioned signal of 16 ± 10. A comparison with a specialized MiCAM Ultimate-L camera has shown that signal-to-noise ratio (SNR) while lower is sufficient for accurate measurements of AP waveform, conduction velocity (± 0.04 m/s) and action potential duration (± 7ms) in mouse and rat hearts. We used 4-aminopyridine to prolong the action potential duration in mouse heart, thus demonstrating that the proposed system is adequate for pharmacological studies.

Priming of rice seed with decoyinine enhances resistance against the brown planthopper Nilparvata lugens

The brown planthopper (BPH), Nilaparvata lugens, is a destructive pest of rice in Asia. The secondary metabolite, decoyinine (DCY), is produced by Streptomyces hygroscopicus. Previous studies on DCY have focused on its antimicrobial and antitumor properties. However, its effect on insect resistance of rice remains unclear. Here, we investigated whether pretreatment of rice seeds with DCY improves plant resistance against BPH. The results showed that rice plants grown from DCY-pretreated seed displayed higher resistance to BPH. Two sex life table analyses revealed that the fecundity, the intrinsic rate of natural increase (rm), the net reproductive rate (R0), the finite capacity of increase (λ) and population size of BPH fed on rice pretreated with DCY significantly decreased compared to the control. The ovary development and the expression level of vitellogenin (NlVg) were decreased in BPH fed on DCY-pretreated rice. Seed priming with DCY significantly increased the duration and number of occurrence of the np, N2, N3 waveforms and decreased the duration of N4-b waveforms of BPH. Additionally, seed priming with DCY also decreased the feeding and oviposition preference of rice to BPH. Therefore, we inferred that seed priming with DCY could enhance rice resistance to BPH.

Short Single-Lead ECG Signal Delineation-Based Deep Learning: Implementation in Automatic Atrial Fibrillation Identification.

Physicians manually interpret an electrocardiogram (ECG) signal morphology in routine clinical practice. This activity is a monotonous and abstract task that relies on the experience of understanding ECG waveform meaning, including P-wave, QRS-complex, and T-wave. Such a manual process depends on signal quality and the number of leads. ECG signal classification based on deep learning (DL) has produced an automatic interpretation; however, the proposed method is used for specific abnormality conditions. When the ECG signal morphology change to other abnormalities, it cannot proceed automatically. To generalize the automatic interpretation, we aim to delineate ECG waveform. However, the output of delineation process only ECG waveform duration classes for P-wave, QRS-complex, and T-wave. It should be combined with a medical knowledge rule to produce the abnormality interpretation. The proposed model is applied for atrial fibrillation (AF) identification. This study meets the AF criteria with RR irregularities and the absence of P-waves in essential oscillations for even more accurate identification. The QT database by Physionet is utilized for developing the delineation model, and it validates with The Lobachevsky University Database. The results show that our delineation model works properly, with 98.91% sensitivity, 99.01% precision, 99.79% specificity, 99.79% accuracy, and a 98.96% F1 score. We use about 4058 normal sinus rhythm records and 1804 AF records from the experiment to identify AF conditions that are taken from three datasets. The comprehensive testing has produced higher negative predictive value and positive predictive value. This means that the proposed model can identify AF conditions from ECG signal delineation. Our approach can considerably contribute to AF diagnosis with these results.

Utilizing smartphone-based electrocardiography and thoracic radiography to evaluate cardiac function and morphology in geriatric Sika deer (Cervus nippon).

To describe qualitative and quantitative cardiothoracic values in geriatric Sika deer (Cervus nippon) using digital radiography, 6-lead ECG (sECG), and smartphone-based ECG (aECG). 10 healthy geriatric Sika deer (9 females and 1 male). Deer were chemically immobilized, thoracic radiographs were obtained, and inhalant anesthesia was initiated. An sECG and aECG were simultaneously recorded for each animal using the same ECG specifications. Results were compared between devices. Radiographically, no deer had any cardiopulmonary abnormalities. Median (range) values for the most important cardiac measurements were 170 (153-193) mm for cardiac height, 135 (122-146) mm for cardiac width, 9 (8-9) for vertebral heart score, and 99 (69-124) mm for cardiosternal contact. All deer had a normal sinus rhythm with no pathological arrhythmias noted. A significant difference between sECG and aECG was identified for minimum heart rate (49 vs 51 beats/min, respectively), P wave duration (0.05 vs 0.03 seconds), P wave amplitude (0.28 vs 0.10 mV), PR interval (0.15 vs 0.12 seconds), and QT interval (0.39 vs 0.30 seconds). Thoracic radiographs were suitable to evaluate basic cardiothoracic morphology in Sika deer. The aECG was useful for assessing heart rate and rhythm but, compared with sECG, proved no substitute for evaluating duration and amplitude of ECG waveforms.

Repellency Mechanism of Natural Guar Gum-Based Film Incorporated with Citral against Brown Planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae).

Using of plant essential oil that coevolved as a defense mechanism against agriculture insects is an alternative means of controlling many insect pests. In order to repel brown planthoppers (BPHs), the most notorious rice insect pest, a new film based on guar gum incorporated with citral (GC film) was formulated, which was effective while being environmentally friendly. In this paper, the effect and mechanism of GC film repellency against BPHs were determined. Repellent activity test and olfactory reaction analysis showed that GC film had repellency effect against BPHs, with repellency of 60.00% and 73.93%, respectively. The result of olfactory reaction indicated that GC film repellency against BPHs relied on smell. EPG analysis showed the proportion and mean duration of np waveform were significantly higher than in CK and increased following the treatment concentration, which indicated that GC film affected the recognition of BPHs to rice. Further analysis by RNA sequencing analysis showed a total of 679 genes were significantly upregulated and 284 genes were significantly downregulated in the BPHs fed on the rice sprayed with GC film compared to control. Odorant-binding protein (OBP) gene 797 and gustatory receptor gene (GR)/odorant receptor (OR) gene 13110 showed a significant decrease in differential expression and significant increase in differential expression, respectively. There were 0.66 and 2.55 differential expression multiples between treated BPHs and control, respectively. According to the results described above, we reasoned that GC film repellency against BPHs due to smell, by release of citral, caused the recognition difficulties for BPHs to rice, and OBP gene 797 and GR/OR gene 13110 appeared to be the crucial candidate genes for GC film repellency against BPHs. The present study depicted a clear and consistent repellency effect for GC film against BPHs and preliminarily clarified the mechanism of GC film as a repellent against BPHs, which might offer an alternative approach for control of BPHs in the near future. Our results could also help in the development and improvement of GC films.

Graph Convolution Networks for Seismic Events Classification Using Raw Waveform Data From Multiple Stations

This letter proposes a multiple station-based seismic event classification model using a deep convolution neural network (CNN) and graph convolution network (GCN). To classify various seismic events, such as natural earthquakes, artificial earthquakes, and noise, the proposed model consists of weight-shared convolution layers, graph convolution layers, and fully connected layers. We employed graph convolution layers in order to aggregate features from multiple stations. Representative experimental results with the Korean peninsula earthquake datasets from 2016 to 2019 showed that the proposed model is superior to the single-station based state-of the-art methods. Moreover, the proposed model significantly reduced false alarms when using continuous waveforms of long duration. The code is available at. <xref ref-type="fn" rid="fn1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">¹</xref>

Frequency-Tunable Pulsed Microwave Waveform Generation Based on Unbalanced Single-Arm Interferometer Excited by Near-Infrared Femtosecond Laser

Femtosecond laser-excited generation of frequency-tunable microwave pulses, based on an unbalanced single-arm interferometer with frequency-to-time mapping, has been proposed and demonstrated with easy-to-obtain commercial devices. The optical wave-to-microwave frequency conversion, which involves continuous tuning in the range from 2.0 GHz to 19.7 GHz, was achieved based on simple spatial–optical group delay adjustment. Additionally, the pulse duration of the microwave waveform was measured to be 24 ns as the length of the linear dispersion optical fiber was fixed at 20 km. In addition, owing to the designs of the single-arm optical path and polarization-independent interference, the generated microwave pulse train had better stability in terms of frequency and electrical amplitude. Furthermore, a near-triangular-shaped microwave pulse at 4.5 GHz was experimentally obtained by the superposition of two generated sinusoidal signals, which verified the potential of this system to synthesize special microwave waveform pulses.

An Experimental Model for the Study of Underwater Pressure Waves on the Central Nervous System in Rodents: A Feasibility Study

Underwater blast differs from blast in air. The increased density and viscosity of water relative to air cause injuries to occur almost exclusively as primary blast, and may cause disorientation in a diver, which may lead to inability to protect the airway and cause drowning. However, cognitive impairments from under water blast wave exposure have not been properly investigated, and no experimental model has been described. We established an experimental model (water shock tube) for simulating the effects of underwater blast pressure waves in rodents, and to investigate neurology in relation to organ injury. The model produced standardized pressure waves (duration of the primary peak 3.5 ms, duration of the entire complex waveform including all subsequent reflections 325 ms, mean impulse 141–281 kPa-ms, mean peak pressure 91–194 kPa). 31 rats were randomized to control (n = 6), exposure 90 kPa (n = 8), 152 kPa (n = 8), and 194 kPa (n = 9). There was a linear trend between the drop height of the water shock tube and electroencephalography (EEG) changes (p = 0.014), while no differences in oxygen saturation, heart rate, S100b or macroscopic bleedings were detected. Microscopic bleedings were detected in lung, intestines, and meninges. Underwater pressure waves caused changes in EEG, at pressures when mild hemorrhage occurred in organs, suggesting an impact on brain functions. The consistent injury profile enabled for the addition of future experimental interventions.

Implantable, Programmable, and Wireless Device for Electrical Stimulation of the Dorsal Root Ganglion in Freely-Moving Rats: A Proof of Concept Study.

ObjectiveThis was a proof of concept study, based on systematic reviews of the efficacy and safety of the dorsal root ganglion (DRG) stimulation. The main objective was to develop an implantable, programmable, and wireless device for electrical stimulation of DRG and a methodology that can be used in translational research, especially to understand the mechanism of neuromodulation and to test new treatment modalities in animal models of pain.MethodsWe developed and tested a stimulator that uses a battery-powered microelectronic circuit, to generate constant current square biphasic or monophasic pulsed waveform of variable amplitudes and duration. It is controlled by software and an external controller that allows radio frequency communication with the stimulator. The stimulator was implanted in Sprague–Dawley (SD) rats. The lead was positioned at the L5 DRG level, while the stimulator was placed in the skin pocket at the ipsilateral side. Forty-five animals were used and divided into six groups: spinal nerve ligation (SNL), chronic compression injury of the DRG (CCD), SNL + active DRG stimulation, intact control group, group with the implanted sham stimulator, and sham lead. Behavioral testing was performed on the day preceding surgery and three times postoperatively (1st, 3rd, and 7th day).ResultsIn animals with SNL, neurostimulation reduced pain-related behavior, tested with pinprick hyperalgesia, pinprick withdrawal test, and cold test, while the leads per se did not cause DRG compression. The rats well tolerated the stimulator. It did not hinder animal movement, and it enabled the animals to be housed under regular conditions.ConclusionA proof-of-concept experiment with our stimulator verified the usability of the device. The stimulator enables a wide range of research applications from adjusting stimulation parameters for different pain conditions, studying new stimulation methods with different frequencies and waveforms to obtain knowledge about analgesic mechanisms of DRG stimulation.

Autonomous on-chip interferometry for reconfigurable optical waveform generation

The generation of user-defined optical temporal waveforms with picosecond resolution is an essential task for many applications, ranging from telecommunications to laser engineering. Realizing this functionality in an on-chip reconfigurable platform remains a significant challenge. Towards this goal, autonomous optimization methods are fundamental to counter fabrication imperfections and environmental variations, as well as to enable a wider range of accessible waveform shapes and durations. In this work, we introduce and demonstrate a self-adjusting on-chip optical pulse-shaper based on the concept of temporal coherence synthesis. The scheme enables on-the-fly reconfigurability of output optical waveforms by using an all-optical sampling technique in combination with an evolutionary optimization algorithm. We further show that particle-swarm optimization can outperform more commonly used algorithms in terms of convergence time. Hence, our system combines all key ingredients for realizing fully on-chip smart optical waveform generators for next-generation applications in telecommunications, laser engineering, and nonlinear optics.

Time-Frequency Characteristics and the Influence Mechanism of the EMR from Coal with Different Joint Angles

It is vital to understand the electromagnetic radiation’s time-frequency characteristics in the process of coal and rock failure with different joint angles in order to reveal the generation mechanism of the electromagnetic radiation (EMR) and improve the accuracy of EMR early warning. We studied the time-frequency characteristics of EMR signals of coal samples with different joint angles. The study finds that, (1) with the increase of joint angle, the failure time and peak load of samples decrease first and increase later, and the postpeak failure time decreases gradually. The EMR counts’ peak value showed a slow rise, a sharp rise, and a slow rise in the three intervals of α = 0° to 45°, 45° to 60°, and 60° to 90°, respectively. The accumulated EMR counts showed a steady upward trend. The duration of the EMR waveform, the dominant frequency of the EMR, and the peak number of the frequency spectrum of coal samples are on the rise. (2) As the joint angle increases, the samples’ failure mode changes from the stage fracture dominated by tension cracks to the rapid fracture with the coexistence of shear and tension cracks and finally to the burst fracture which produces a large number of fragments. This is also the main reason for the difference of the EMR generation mechanism and the signal of samples with different joint angles. (3) According to the experimental results, we established the modified formulas for calculating the EMR threshold value and deviation of coal and rock with joints under different stress environments and revealed that the longer the EMR waveform duration, the higher the dominant frequency, and the more the number of spectrum peaks, the greater the burst risk of coal and rock.