Time Delay Difference Research Articles

High-accuracy detection and location of gas leaks based on adaptive weighted data fusion using an ultrasonic transducer array

This paper proposes a gas leak detection and location method with high accuracy based on an adaptive weighted data fusion algorithm using an ultrasonic transducer array. First, the approximate entropy theory is combined with a support vector machine (SVM) to judge whether there is a gas leak, achieving a recognition accuracy of 95.69%. Once a leak is identified, a leak localisation algorithm is applied. To obtain more stable features and reduce environmental noise, the sound pressure amplitude and time-delay difference are extracted using an optimised signal processing method and normalised least mean squares (NLMS) adaptive filter, respectively. The energy decay (ED) localisation algorithm is then fused with the time difference of arrival (TDOA) algorithm to determine the location of the leak. Experimental results demonstrate that under a pressure of 15 kPa in the measured container with a distance of 1 m between the leak and transducer array, the location error is within 5 mm, which is more accurate than previously proposed methods. Additionally, the adaptive weighted data fusion algorithm overcomes the limitations of the TDOA and ED algorithms.

Numerical Simulation on Medium-Deep Hole Straight Cut Blasting Based on the Principle of Segmented Charging

The efficiency of rock excavation depends on cut blasting. However, medium-deep hole cutting blasting faces the challenges of large clamping action and unsatisfactory blasting efficiency. The study proposes sectional charge cutting blasting technology and analyzes the mechanism of cavity formation by establishing a numerical model. The results demonstrated that sectional charge blasting in the hole can expand the range of stress waves, and the segment interaction is also optimized by introducing a delay time difference. These factors contribute to an increase in the rock-breaking volume and an improvement in the degree of rock breaking. Furthermore, the cutting effects of different segmented proportional models are quantified. When the upper and lower sections are symmetrically charged, the damage range caused by the upper section is greater. The reason is that the clamping force exerted on the rock mass increases with the depth of the hole. In addition, when the upper section ratio is 0.4, the model exhibits the most excellent cavity volume; this results from charging according to the symmetry principle for optimal energy distribution.

Suppression of Combustion Oscillations in Hydrogen-Enriched Can-Type Combustors Through Fuel Staging

Abstract To achieve decarbonization in power-generating gas turbines, the technology of mixing hydrogen with natural gas is garnering significant attention. However, when blending natural gas with hydrogen, the altered combustion characteristics can lead to combustion instability in gas turbine combustors. Although fuel staging can effectively suppress combustion instability for can-type combustors, further research on mitigation strategies for hydrogen cofiring and their predictive methods is required. This study involves hydrogen cofiring experiments using a full-scale can-type combustor. Moreover, the resulting suppression of combustion instability is analyzed through fuel staging by utilizing three-dimensional (3D) computational fluid dynamics (CFD) and one-dimensional (1D) thermo-acoustic analysis. The experiments used a full-scale industrial can-type combustor with a five-around-one nozzle configuration. Hydrogen was blended with natural gas up to a volume fraction of 30%, maintaining a constant thermal power. Fuel staging was applied by controlling two out of five outer nozzles (ONs) along with the remaining three. Before the 1D thermo-acoustic analysis, the internal flame structure of the combustor was examined through 3D CFD analysis. Based on the results, a multi-input multi-output (MIMO) system was constructed for 1D thermo-acoustic analysis of the can-type combustor. The application of time delays derived from 3D CFD analysis to the 1D model revealed that differences in flame time delays across the nozzles cause combustion instability suppression observed in fuel staging.

Delay propagation patterns in Japan’s domestic air transport network

We experience air traffic delays every day, but are there any recurrent patterns in these delays? In this study, we investigate the recurrence of delay propagation patterns in Japan’s domestic air transport network in 2019 by integrating delay causality networks and temporal network analysis. Additionally, we examine characteristics unique to delay propagation by comparing delay causality networks with corresponding randomized networks generated by a directed configuration model. As a result, we found that the structure of the delay propagation patterns can be classified into several groups. The identified groups exhibit statistically significant differences in total delay time and average out-degree, with different airports playing central roles in spreading delays. The results also suggest that some delay propagation patterns are particularly prominent during specific times of the year, which could be influenced by Japan’s seasonal and geographical factors. Moreover, we discovered that specific network motifs appear significantly more (or less) frequently in delay causality networks than their corresponding randomized counterparts. This characteristic is particularly pronounced in groups with more significant delays. These results suggest that delays propagate following specific directional patterns, which could significantly contribute to predicting air traffic delays. We expect the present study to trigger further research on recurrent and non-recurrent natures of air traffic delay propagation.

A high-order time-delay difference estimation method for signal enhancement in the distorted towed hydrophone array.

In passive sonar systems, deviations from an ideal linear configuration can significantly impair the beamforming performance of towed hydrophone arrays. This paper presents a method aimed at improving the underwater acoustic signals in the presence of array distortion. The method is centered on a high-order time-delay difference estimation technique utilizing time-frequency autofocus. Initially, a detailed signal model is established that captures the distinctive characteristics of distorted arrays. Subsequently, an algorithm is introduced for high-order time-delay difference estimation to enhance signal fidelity by leveraging phase information within narrowband components originating from incidental acoustic sources. Additionally, a quality metric to evaluate these components is introduced, facilitating the practical implementation of the method. The effectiveness of the proposed approach is validated through both simulation and experimental results, demonstrating its superiority over existing techniques. Importantly, this method does not require prior knowledge of the distortion pattern, making it adaptable to various non-linear array configurations.

Dynamic mater-slave control strategy for transient coordination of inverter based microgrids under asymmetric faults

The ever-expanding inverter-based microgrids (MGs) require the grid-forming distributed renewable energy resources (DERs) to enhance the system safety. However, the different types of grid-forming DERs are prone to have transient conflicts with each other under short circuit faults, leading to unexpected outage or even system collapse. The fast response and poor overcurrent capability of DERs make transient coordination a challenge. This paper proposes a dynamic master–slave architecture for transient coordination control in islanded MGs under asymmetric faults. A dynamic reconfigurable voltage reference unit (DVRU) is designed according to the real faults. In this manner, the other DERs could comply with this DVRU to achieve both system voltage support, inrush current restraining, and power oscillation suppression. It is action signals instead of phase signals need to be transferred by the communication bus with the proposed local fault current differential time delay method (FCDDM). Thus, the low-bandwidth and the enhanced robust communication could be met under transient state. Additionally, the feasibility of the proposed method to combined with relay protection is analyzed. Finally, case study results on islanded MGs consisting of various grid-forming and grid-following DERs demonstrate the effectiveness and robustness of the proposed method under short circuit faults as well as communication failures.

Dynamic response characteristics of backfill under blasting disturbance simulated through a three-dimensional model

During mining operations, the backfill body is subject to significant disturbance due to large-volume blasting, resulting in stress concentration and vibration response within the backfill. This alters energy distribution, leading to the continuous development, expansion, and accumulation of damage, potentially culminating in instability and collapse. Blasting disturbance in stopes is the main cause of filling instability and ore dilution. It is crucial to study the failure mechanism of filling bodies under blasting load to guide actual mine production. In this study, a custom mold was created to establish an innovative three-dimensional model of an ore-backfill system subject to explosion loading. Simultaneous detonation was selected as the control group and delayed detonation was selected as the experimental group. Monitoring and analysis methods, such as a high-speed camera system, MATLAB software, and vibration monitors, were utilized to investigate the impact of delay time on the dynamic response characteristics of the backfill. The results show that the dynamic fracture process of the backfill is mainly divided into four stages: initial crack initiation stage, crack development stage, crack expansion stage, and backfill collapse stage. The difference in delay time on the dynamic fracture process of the backfill is mainly reflected in two aspects: time effect and crack distribution. The surface flatness after delayed detonation is higher by 20.5 % as compared with that after simultaneous detonation. The average damping rate during delayed detonation decreases by 19.7 % as compared with that after simultaneous detonation, the frequency distribution of the single stage is more uniform, and the instantaneous peak energy during delayed detonation is 0.76 times that during simultaneous detonation. The maximum crushing size, average crushing size, and bulk crushing size after delayed detonation are reduced by 25 %, 15.26 %, and 9.23 %, respectively, compared with that after simultaneous blasting. Thus, delayed detonation effectively improves the crushing effect while reducing the degree of damage to the backfill.

Sex differences in delay times in ST-segment elevation myocardial infarction: A cohort study

BackgroundThe present study analyzes a cohort of consecutive patients with ST-segment elevation acute myocardial infarction (STEMI), evaluating the ischemia–reperfusion times from the perspective of gender differences (females versus males), with a long-term follow-up. MethodsSingle-center analytical cohort study of patients with STEMI in a tertiary hospital, between January 2015 and December 2020. ResultsA total of 2668 patients were included, 2002 (75%) men and 666 (25%) women. The time elapsed from the onset of symptoms to the opening of the artery was 197min (IQR 140–300) vs 220min (IQR 152–340), p=0.004 in men and women respectively. A delay in health care significantly impacts the occurrence of cardiovascular adverse events at follow-up, HR 1.34 [95%CI 1.06–1.70]; p=0.015. ConclusionsWomen took longer to go to health care services and had a longer delay both in the diagnosis of STEMI and in coronary reperfusion. It is imperative to emphasize the necessity of educating women about the recognition of ischemic heart disease symptoms, empowering them to raise early alarms and seek timely medical attention.

The mechanism for directional hearing in fish

Locating sound sources such as prey or predators is critical for survival in many vertebrates. Terrestrial vertebrates locate sources by measuring the time delay and intensity difference of sound pressure at each ear1–5. Underwater, however, the physics of sound makes interaural cues very small, suggesting that directional hearing in fish should be nearly impossible6. Yet, directional hearing has been confirmed behaviourally, although the mechanisms have remained unknown for decades. Several hypotheses have been proposed to explain this remarkable ability, including the possibility that fish evolved an extreme sensitivity to minute interaural differences or that fish might compare sound pressure with particle motion signals7,8. However, experimental challenges have long hindered a definitive explanation. Here we empirically test these models in the transparent teleost Danionella cerebrum, one of the smallest vertebrates9,10. By selectively controlling pressure and particle motion, we dissect the sensory algorithm underlying directional acoustic startles. We find that both cues are indispensable for this behaviour and that their relative phase controls its direction. Using micro-computed tomography and optical vibrometry, we further show that D. cerebrum has the sensory structures to implement this mechanism. D. cerebrum shares these structures with more than 15% of living vertebrate species, suggesting a widespread mechanism for inferring sound direction.

Sex differences in delay times in ST-segment elevation myocardial infarction: A cohort study

BackgroundThe present study analyzes a cohort of consecutive patients with ST-segment elevation acute myocardial infarction (STEMI), evaluating the ischemia–reperfusion times from the perspective of gender differences (females versus males), with a long-term follow-up. MethodsSingle-center analytical cohort study of patients with STEMI in a tertiary hospital, between January 2015 and December 2020. ResultsA total of 2668 patients were included, 2002 (75%) men and 666 (25%) women. The time elapsed from the onset of symptoms to the opening of the artery was 197min (IQR 140–300) vs 220min (IQR 152–340), p=0.004 in men and women respectively. A delay in health care significantly impacts the occurrence of cardiovascular adverse events at follow-up, HR 1.34 [95%CI 1.06–1.70]; p=0.015. ConclusionsWomen took longer to go to health care services and had a longer delay both in the diagnosis of STEMI and in coronary reperfusion. It is imperative to emphasize the necessity of educating women about the recognition of ischemic heart disease symptoms, empowering them to raise early alarms and seek timely medical attention.

Recognition method for biomimetic camouflage communication signal imitating cetacean click in underwater multipath channels

Focusing on the need of biomimetic camouflage communication signal recognition in underwater multipath channels, we propose a recognition method for biomimetic camouflage click communication train (BCCCT) based on time delay difference (TDD) coding in multipath channels. For the problem of multipath interference, we perform multipath determination on the received signal by autocorrelation, filter relevant peak points, determine the time delays between multipaths, and remove the multipath interference signals according to the determined time delays. A click extraction method based on the double sliding window is proposed, which locates the boundary of click by signal envelope. By analyzing the distribution characteristics of the time interval of adjacent clicks (TIAC) of BCCCT and real click train (RCT), we model the TIACs based on Gaussian kernel probability density estimation (PDE), and recognize the BCCCTs by the Convolutional Neural Networks (CNN), which takes the PDE curve as the system input. The numerical simulations and a lake experiment are carried out to measure the effectiveness of the recognition method proposed under different signal-to-noise ratios (SNR), coding parameters, and channels. The recognition accuracy can achieve 80 % at 0 dB in the constructed channels. Moreover, in the real underwater communication environment, the recognition accuracy can achieve 95 %.

Changes in hamstring contractile properties during the competitive season in young football players.

The study aimed to examine alterations and imbalances in hamstring muscle contractile properties among young football players throughout their competitive season, and to understand how these changes might contribute to the risk of muscle injuries. Hamstring injuries are particularly common in football, yet the underlying causes and effective prevention methods remain unclear. The research involved 74 young footballers who were assessed before the season (pre-test) and after 12 weeks of training (post-test). To evaluate changes in hamstring muscle contractile properties, specifically the left and right biceps femoris (BF) and semitendinosus (ST), tensiomyography (TMG) parameters were utilized. In comparison to the BF muscle, significant differences in time delay (Td) between the left and right sides in the post-test (p = 0.0193), and maximal displacement (Dm) between the left and right sides at the pre-test (p = 0.0395). However, significant differences in Dm were observed only in the left ST muscle between the pre- and post-tests (p = 0.0081). Regarding lateral symmetry, BF registered measurements of 79.7 ± 13.43 (pre-test) and 77.4 ± 14.82 (post-test), whereas ST showed measurements of 87.0 ± 9.79 (pre-test) and 87.5 ± 9.60 (post-test). These assessments provided TMG reference data for hamstring muscles in young footballers, both before the season and after 12 weeks of in-season training. The observed changes in the contractile properties and decrease in lateral symmetry of the BF in both tests suggest an increased risk of injury.

Guided Lamb Wave Array Time-Delay-Based MUSIC Algorithm for Impact Imaging.

Composite materials, valued in aerospace for their stiffness, strength and lightness, require impact monitoring for structural health, especially against low-velocity impacts. The MUSIC algorithm, known for efficient directional scanning and easy sensor deployment, is gaining prominence in this area. However, in practical engineering applications, the broadband characteristics of impact response signals and the time delay errors in array elements' signal reception lead to inconsistencies between the steering vector and the actual signal subspace, affecting the precision of the MUSIC impact localization method. Furthermore, the anisotropy of composite materials results in time delay differences between array elements in different directions. If the MUSIC algorithm uses a fixed velocity value, this also introduces time delay errors, further reducing the accuracy of localization. Addressing these challenges, this paper proposes an innovative MUSIC algorithm for impact imaging using a guided Lamb wave array, with an emphasis on time delay management. This approach focuses on the extraction of high-energy, single-frequency components from impact response signals, ensuring accurate time delay measurement across array elements and enhancing noise resistance. It also calculates the average velocity of single-frequency components in varying directions for an initial impact angle estimation. This estimated angle then guides the selection of a specific single-frequency velocity, culminating in precise impact position localization. The experimental evaluation, employing equidistantly spaced array elements to capture impact response signals, assessed the effectiveness of the proposed method in accurately determining array time delays. Furthermore, impact localization tests on reinforced composite structures were conducted, with the results indicating high precision in pinpointing impact locations.

Sex differences in the pre-hospital ambulance delay, assessment and treatment of patients with acute coronary syndrome: a rapid evidence review.

Chest pain is a frequent symptom suffered by adult patients attended by ambulance. Evidence suggests female patients may suffer different symptoms to their male counterparts, potentiating differences in pre-hospital time delays, assessment and treatment. To explore the sex differences in the pre-hospital ambulance delay, assessment and treatment of patients with acute coronary syndrome (ACS). A rapid evidence review was conducted following the Cochrane rapid review guidelines. MEDLINE and CINAHL Complete were searched via EBSCOhost on 2 February 2023, and reference lists of included studies and reviews were screened. The Joanna Briggs Institute checklist for analytical cross-sectional studies was used to perform critical appraisal, and a narrative synthesis was conducted. From 216 articles screened, nine were included, representing over 3.1 million patients from five different countries. Female patients were more likely to suffer delays in time to first electrocardiogram (ECG) and delays in transport time to the emergency department by ambulance. Female patients were also less likely to receive an ECG, aspirin, glyceryl trinitrate and other analgesics. There are sex disparities in the pre-hospital ambulance delay, assessment and treatment of patients with ACS. Future research is urgently needed to fully understand the reasons for these observations.

High-dimensional single photon based quantum secure direct communication using time and phase mode degrees

Quantum secure direct communication (QSDC) can guarantee security using the characteristics of quantum mechanics even when a message is directly transmitted through a quantum channel without using a secret key. However, the transmission rate of the QSDC is limited by the dead time of a single photon detector (SPD) as well as channel loss over the distance. To overcome this limited transmission rate, we propose a high-dimensional single photon-based QSDC protocol that applies two optical degrees of freedom: time and phase state. First, an N-dimensional time and phase state generation method that considers the dead time is proposed to minimize the measurement loss of a transmitted message. Second, among the two types of quantum states, the phase state with relatively low measurement efficiency is used only for eavesdropping detection, and the time state is used for sending messages with differential delay time bin-based encoding techniques. Lastly, we propose an efficient method for measuring N-dimensional time and phase-based quantum states and recovering classical bit information. This study performs security analysis against various attacks, and verifies the transmission rate improvement effect through simulation. The result indicates that our proposal can guarantee higher security and transmission rates compared to the conventional DL04 QSDC.

Multistatic Target Localization in Absence of Transmitter Position Using Differential Time Delay Measurements

Multistatic Target Localization in Absence of Transmitter Position Using Differential Time Delay Measurements

Experimental research on signal sensing of distributed acoustic sensing optical fiber based on Φ-OTDR in shallow water

The distributed acoustic sensing (DAS) technology based on phase-sensitive optical time domain reflectometry (Φ-OTDR) has been widely and well applied on land. Meanwhile, the distributed acoustic sensing optical fiber (DASF) based on Φ-OTDR, as a new type of sensor, is still in the initial stage of research, gets much attention in recent years because of its long-distance monitoring, high sensitivity, anti-electromagnetic interference, good concealment and so on. Performances of DASF in sensing different kinds of acoustic source signals were given by experiments in shallow water, which included single frequency pulse signal in the fixed position, the moving single frequency continuous pulse signal, the moving broadband signal, and the signal generated by the sailing surface target. Depth of the active sound source was changed to examine the performance of DASF in sensing signals in different depths. The specific experimental process was given, and the experimental results were processed and analyzed. Additionally, wave components of data generated from of the sailing surface vessel were explored with the time delay difference between the equivalent array elements of DASF. Results show that DASF can sense the above varieties of underwater acoustic signals well, and the physical field generated by the sailing surface vessel in shallow water include acoustic field and flow field, in which the propagation velocity of the former is faster than that of the latter.

Modified Frequency-Sliding Generalized Cross Correlation for Time Delay Difference Estimation of Microphone Array

Modified Frequency-Sliding Generalized Cross Correlation for Time Delay Difference Estimation of Microphone Array

A Deep-Sea Broadband Sound Source Depth Estimation Method Based on the Interference Structure of the Compensated Beam Output

This paper proposes an underwater broadband target depth estimation method based on the multipath arrival structure in medium and short-range deep-sea environments. The proposed approach involves separating the multipath rays arriving at the vertical line array using the matched filtering technique. The combined beamforming is then applied to the vector hydrophone vertical array (VHVA) to obtain more accurate elevation angle estimates. The components of the interference sound field at different distances are judged, and the signal received by the array is compensated using suitable estimated angles. Finally, the multipath time delay difference is extracted from the pulse peaks of the compensated signal, and the target depth is estimated by establishing the relationship among the multipath time delay difference, the elevation angle and depth. Simulations and experiments demonstrate the effectiveness of this method in reducing the depth estimation bias and avoiding the misjudgment of surface or submerged targets.

Experimental Measurements of Ignition Delay Times of Iso-octane/n-Butanol Blend Mixtures in Rapid Compression Machine (RCM)

Among oxygenated alternative fuels, n-butanol is considered as a promising alternative biofuel which can partially (or fully) replace conventional transportation fuels currently in use. However, before n-butanol can be commercially utilised, its fundamental combustion characteristics need to be fully understood. In this work, the effect of adding n-butanol on autoignition property of iso-octane was studied. Measurements of ignition delay times for the two blends of n-butanol proportions of 30% and 50% by mole weight were made in a Rapid Compression Machine for stoichiometric mixtures at 2.0 MPa and temperature range 651-918 K. n-butanol increased ignition delay times of iso-octane at lower temperatures and hence acted as an octane enhancer, while at higher temperatures delay times were reduced. In the intermediate temperatures there was visually no difference in delay times between the two blends. Throughout the temperature range studied, the delay times of both blends were much closer to those of pure n-butanol which suggests that the combustion chemistry of n-butanol was dominant over that of iso-octane. These results have shown that n-butanol can enhance fuel octane rating and therefore can potentially improve thermal efficiency of SI engines, whilst CI engines can benefit from the reduced delay times at higher temperatures.