Typical Delay Time Research Articles

A Comparative Study of Multi-Rotor Unmanned Aerial Vehicles (UAVs) with Spectral Sensors for Real-Time Turbidity Monitoring in the Coastal Environment

Complex coastal environments pose unique logistical challenges when deploying unmanned aerial vehicles (UAVs) for real-time image acquisition during monitoring operations of marine water quality. One of the key challenges is the difficulty in synchronizing the images acquired by UAV spectral sensors and ground-truth in situ water quality measurements for calibration, due to a typical time delay between these two modes of data acquisition. This study investigates the logistics for the concurrent deployment of the UAV-borne spectral sensors and a sampling vessel for water quality measurements and the effects on the turbidity predictions due to the time delay between these two operations. The results show that minimizing the time delay can significantly enhance the efficiency of data acquisition and consequently improve the calibration process. In particular, the outcomes highlight notable improvements in the model’s predictive accuracy for turbidity distribution derived from UAV-borne spectral images. Furthermore, a comparative analysis based on a pilot study is conducted between two multirotor UAV configurations: the DJI M600 Pro with a hyperspectral camera and the DJI M300 RTK with a multispectral camera. The performance evaluation includes the deployment complexity, image processing productivity, and sensitivity to environmental noises. The DJI M300 RTK, equipped with a multispectral camera, is found to offer higher cost-effectiveness, faster setup times, and better endurance while yielding good image quality at the same time. It is therefore a more compelling choice for widespread industry adoption. Overall, the results from this study contribute to advancement in the deployment of UAVs for marine water quality monitoring.

Gray skyhook predictive control of magnetorheological semi-active seat suspension with time delay

Semi-active seat suspension with a magnetorheological (MR) damper has been a popular study issue in recent years. Since the response time delay of the MR damper can reduce the control effect and even make the vibration more severe, there is an urgent need to compensate for the response time delay. In this paper, gray prediction is introduced into the vibration control study of commercial vehicle seat suspension. A gray skyhook prediction controller is designed to compensate for the response time delay. This proposed controller does not rely heavily on controller parameter optimization and requires fewer state variables than other typical time delay compensation controllers. The mechanical property of the MR damper has been tested, modeled, and analyzed. A seat suspension dynamic model considering geometric nonlinearity is established based on the motion relationship between the components of the suspension. Subsequently, the effect of the response time delay on seat suspension vibration control has been verified by simulation. The results show that the control effect deteriorates significantly after considering the response time delay. Finally, prediction accuracy and vibration reduction performance of the designed gray skyhook predictive controller are verified by simulation and bench testing. The results illustrate that the gray skyhook predictive controller provides excellent time delay compensation and can significantly improve the ride comfort and handling stability of the driver. This study provides a reference for vibration control research of the MR seat suspension.

Impulse and Plasma Plume Generated By Ablating Aluminum Target with Nanosecond Laser in Double-Pulse Configuration

For laser ablation propulsion, the enhancement of the impulse is very challenging to realize without increasing the laser energy. In this paper, the enhancement of the impulse in vacuum is achieved by laser ablation in double-pulse mode. The impulse produced by irradiating the aluminum target for different energy combinations in double-pulse mode was measured with the torsion pendulum. The plasma plume was observed at the same time by fast photography to analyze the cause of the impulse characteristics. The effect of the energy combinations for double-pulse mode on the ablation impulse was investigated at typical interpulse delay time. When the delay time between the pulses is set to 80 ns, the maximum impulse is increased by approximately 11% compared to that of the single-pulse mode at the same total energy, wherein the energy of the first pulse is 125mJ in total energy of 200mJ. Therefore, the enhancement of the impulse can be achieved by choosing the suitable energy combination in the double-pulse configuration. However, when the time delay is 300ns, the difference in energy combinations has little influence on the impulse. The results reported here provide guidance for the application of laser ablation propulsion in space.

Time delays and pollution in an open‐access fishery

AbstractWe analyze the impacts of pollution on fishery sector using a dynamical system approach. The proposed model presupposes that the economic development causes emissions that either remediate or accumulate in the oceans. The model possesses a block structure where the solutions of the rate equations for the pollutant and the economic activity act as an input for the biomass and effort equation. We also account for distributed delay effects in both the pollution level and the economic activity level in our modeling framework. The weight functions in the delay terms are expressed in terms of exponentially decaying functions, which in turn enable us to convert the modeling framework to a higher‐order autonomous dynamical system by means of a linear chain trick. When both the typical delay time for the economic activity and the typical delay time for the pollution level are much smaller than the biomass time scale, the governing system is analyzed by means of the theory for singularly perturbed dynamical systems. Contrary to what is found for population dynamical systems with absolute delays, we readily find that the impact of the distributed time lags is negligible in the long‐run dynamics in this time‐scale separation regime. Recommendations for Resource Managers Resource managers should be aware of the dynamical interrelations between fisheries and pollution, also those that are time delayed. Time lags between biological, economic, and environmental variables are affecting the time paths of these variables. In the long run, the impact from distributed time lags have a negligible influence on the long‐run dynamical evolution. Neither the past history of economic activities nor the past history of pollution growth can affect the fishery dynamics in the long run. More empirical and theoretical research are needed to increase our understanding of the interrelation between fisheries and pollution.

Detecting cosmic strings with lensed fast radio bursts

Correlated red noise recently reported from pulsar timing observations may be an indication of stochastic gravitational waves emitted by cosmic strings that formed during a primordial phase transition near the grand unification energy scale. Unfortunately, known probes of cosmic strings, namely the cosmic microwave background anisotropies and string lensing of extragalactic galaxies, are not sensitive enough for low dimensionless string tensions of $G\ensuremath{\mu}{c}^{\ensuremath{-}2}={10}^{\ensuremath{-}10}\ensuremath{-}{10}^{\ensuremath{-}7}$ (where the tension $\ensuremath{\mu}$ is the string energy per unit length) that are needed to explain this putative signal. We show that strong gravitational lensing of fast radio bursts (FRBs) by cosmic strings is a potentially unambiguous avenue to probe that range of string tension values. The image pair of string lensing are expected to have identical magnification factor and parity, and have a typical time delay of $\ensuremath{\sim}{10}^{2}(G\text{ }\ensuremath{\mu}\text{ }{c}^{\ensuremath{-}2}/{10}^{\ensuremath{-}8}{)}^{2}\text{ }\text{ }\mathrm{s}$. The unique spectral fingerprint of each FRB, as well as the possibility to detect correlations in the time series of the electric field of the radio waves, will enable verification of the string lensing interpretation. Very-long-baseline interferometry observations can spatially resolve the image pair and provide a lower bound on the string tension based on the image separation. We calculate the FRB lensing rate as a function of the FRB detection number for several different models of the FRB redshift distribution. We find that a survey detecting $\ensuremath{\sim}{10}^{5}$ FRBs, in line with estimates for the detection rate of the forthcoming survey CHORD, can uncover a strong lensing event for a string tension of $G\ensuremath{\mu}\text{ }{c}^{\ensuremath{-}2}\ensuremath{\simeq}{10}^{\ensuremath{-}7}$. Larger FRB surveys, such as Phase 2 of the Square Kilometre Array, have the potential to significantly improve the sensitivity on the string tension to $G\ensuremath{\mu}\text{ }{c}^{\ensuremath{-}2}\ensuremath{\simeq}{10}^{\ensuremath{-}9}$.

Implicit Periodic Strong Reflection Points of UWB Hilbert Fractal Time Delay Lines and the Performance Improvements

The serpentine delay line (SDL) is commonly used as one kind of typical true time delay lines (TDLs) with periodic strong reflection points (SRPs). However, the Hilbert fractal curve delay lines (HFCDLs), with the same circuit area and the same spacing between the adjacent segment lines, are proven to have quite different SRPs with improved performance. An analytic analysis model is used to investigate the SRPs of the two-order and three-order HFCDLs, respectively, in which the structure symmetry is fully considered to make the relevant adjacent structure equivalent to a pair of parallel dual lines. Thus, the accumulated far-end crosstalk (FEXT) is derived in the HFCDLs, and the implicit periodic SRPs are revealed. Furthermore, the iterated two-order and three-order HFCDLs are investigated to validate the analysis model. Subsequently, the periodically loaded transmission line (PLTL) with and without strategic discontinuous structured guard lines (DSGLs) is, respectively, utilized in the three-order and two-order HFCDLs, and thus, the proposed structures possess better wideband cancelation of the FEXT accordingly. In the ultrawideband (UWB) range of dc–51 GHz, the typical return loss (RL) is less than 20 dB for the proposed two-order HFCDL and less than 15 dB for the proposed three-order HFCDL. Meanwhile, the fluctuations are eliminated in the group delay (GD) for the proposed two-order HFCDL. For the proposed three-order HFCDL, the delay fluctuations are observed at the high end of the UWB due to the enhanced near-end crosstalk (NEXT), while the delay fluctuations less than 72.2 ps are still obtained in the range of dc–35 GHz.

Exotic image formation in strong gravitational lensing by clusters of galaxies – III. Statistics with HUDF

ABSTRACT We study the image formation near point singularities (swallowtail and umbilics) in the simulated strongly lensed images of Hubble Ultra Deep Field (HUDF) by the Hubble Frontier Fields (HFF) clusters. In this work, we only consider nearly half of the brightest (a total of 5271) sources in the HUDF region. For every HFF cluster, we constructed 11 realizations of strongly lensed HUDF with an arbitrary translation of the cluster centre within the central region of HUDF and an arbitrary rotation. In each of these realizations, we visually identify the characteristic/exotic image formation corresponding to the different point singularities. We find that our current results are consistent with our earlier results based on different approaches. We also study time delay in these exotic image formations and compare it with typical five-image geometries. We find that the typical time delay in exotic image formations is an order of magnitude smaller than the typical time delay in a generic five-image geometry.

Optimal Calculation Method of Mean Equivalent Diameter of Floc Particles Based on MCC

In the process of water treatment, coagulation is an important process to remove minerals and organic particles from raw water, which has typical time delay and nonlinearity. The effect of coagulation directly affects the turbidity of the effluent. According to the good correlation between the mean equivalent diameter of floc particles and the turbidity of effluent water, the image processing method is used to preprocess the floc image, the parameters of floc particles are quantitatively analyzed, and the mean equivalent diameter of floc particles is obtained, which is used as one of the bases for the control of coagulant dosage. However, no matter whether the coagulation process in actual situations interferes with the outside world or not, the equivalent diameters of floc particles after coagulation may have abnormal and invalid values, which may lead to a problem that there is a large difference between the mean equivalent diameter of floc particles calculated by a least square method and the mean valid equivalent diameter of floc particles. In response to this problem, this article proposes an optimal calculation method of the mean equivalent diameter of floc particles based on the maximum correntropy criterion (MCC) to reduce the negative impact of the abnormal and invalid equivalent diameters of floc particles on the mean equivalent diameter and provide an important reference data for the precise dosing control of coagulants. Finally, the feasibility of the theoretical results is verified by several numerical experiments.

Investigation of the fluid dynamic of the modified Hartmann tube equipment by high-speed video processing

Hartmann tube equipment is used in the dust explosion experimental test to screen the flammability of powdered materials (according to ISO 80079-20) and to determine the Minimum ignition energy of dust (UNI EN 13824:2004). For the test, the nominal concentration, as the ratio between the dust sample mass and the chamber test volume (1.2 liters), is considered, assuming a uniform concentration distribution. Even though adopted as standard procedure, this approach does not consider the dust cloud's non-stationary conditions inside the tube: the effect of turbulence decrease and dust sedimentation during the test duration will affect the dust concentration locally and globally within the test enclosure. Moreover, it is well known that the turbulence intensity influences Minimum Ignition Energy.This work derives from previous investigation on describing the dust cloud behavior within dust explosibility laboratory apparatuses. High-speed video recordings have recently been adopted to support the dust cloud dynamic analysis and visualize the cloud dispersion within a standard test setup, as the 20 L sphere and the modified Hartmann tube. This work intends to use different high-speed videos of dust dispersions in the modified Hartmann tube, with different injection pressure and sample mass, to focus on the behavior of the cloud at the typical delay time of the MIE measurement, i.e., 60-180 ms. Each video is processed frame by frame to reveal information on the cloud dynamics, otherwise hidden. The dust dynamic is accounted for calculating the variation in time of the brightness of pixels.This way, it is possible to obtain a set of data that incorporate the effects of the dust cloud distribution and the velocity of the particles’ clusters. The experimental data processing will help to focus on the time-scale and the length scale of the turbulence. The next study will focus on evaluating the time and space scale of the dust cloud and identifying the effect of ignition time delay on the MIE measurement to provide indications to operate at the most conservative conditions (higher concentration) and to avoid issues and under/overestimates due to agglomeration, sedimentation or segregation of dust particles.

Heavy Double Neutron Stars: Birth, Midlife, and Death

Abstract Radio pulsar observations probe the lives of Galactic double neutron star (DNS) systems while gravitational waves enable us to study extragalactic DNS in their final moments. By combining measurements from radio and gravitational-wave astronomy, we seek to gain a more complete understanding of DNS from formation to merger. We analyze the recent gravitational-wave binary neutron star mergers GW170817 and GW190425 in the context of other DNS known from radio astronomy. By employing a model for the birth and evolution of DNS, we measure the mass distribution of DNS at birth, at midlife (in the radio), and at death (in gravitational waves). We consider the hypothesis that the high-mass gravitational-wave event GW190425 is part of a subpopulation formed through unstable case BB mass transfer, which quickly merge in ∼10–100 Myr. We find only mild evidence to support this hypothesis and that GW190425 is not a clear outlier from the radio population as previously claimed. If there are fast-merging binaries, we estimate that they constitute 8%–79% of DNS at birth (90% credibility). We estimate the typical delay time between the birth and death of fast-merging binaries to be ≈5–401 Myr (90% credibility). We discuss the implications for radio and gravitational-wave astronomy.

Quantitative Tuning of Active Disturbance Rejection Controller for FOPTD Model With Application to Power Plant Control

Active disturbance rejection controller (ADRC) has achieved soaring success in motion controls featured by rapid dynamics. However, it turns obstreperous to implement it in the power plant process with considerable time-delay, largely because of the tuning difficulty. To this end, this article proposes a quantitative tuning rule for the time-delayed ADRC (TD-ADRC) structure based on the typical first order plus time delay (FOPTD) model. By compensating the FOPTD process as an integrator plus time delay in low frequencies, the gain parameter of TD-ADRC can be related to a scaled time constant which shapes the closed-loop tracking performance. Bandwidth parameter of extended state observer is scaled as a dimensionless parameter. A sufficient stability condition of TD-ADRC is theoretically derived in terms of the scaled parameter pair, the range of which falls within the practical interest. Relative delay margin is revealed as a critical robustness metric among others, a default pair of scaled parameter setting is recommended as well as an explicit retuning guideline according to the user's preference for performance or robustness. Simulation and laboratory water tank experiment validate the tuning efficacy and a coal mill temperature control test depicts a promising prospective of the proposed method in process control practice.

Measurement accuracy and spatial resolution of a distributed temperature sensor based on a two-pulse differential coherent reflectometer

We present a model and numerical simulation of a distributed temperature sensor based on a two-pulse differential coherent optical time-domain reflectometer (COTDR). The differential phase measured using a phase-sensitive Rayleigh reflectometer is shown to have a regular component, which is a linear function of temperature, and a random component, which is related to a random distribution of scattering centres in the fibre and restricts the accuracy of measurements of variations in temperature. Measurement accuracy can be improved by reducing the relative contribution of the random component via a decrease in pulse duration and/or an increase in the time delay between pulses. The spatial resolution of a differential two-pulse phase-sensitive reflectometer is shown to be determined by the time delay between pulses and to vary little with pulse duration. At a typical pulse duration (200 ns) and delay time (300 ns), the accuracy in measurements of variations in temperature in the 0.1-K range is 2 % and the spatial resolution is about 30 m.

THE TIME DELAY OF AIR/OXYGEN MIXTURE DELIVERY AFTER THE CHANGE OF SET FIO2: AN IMPROVEMENT OF A NEONATAL MATHEMATICAL MODEL

<p>Oxygen therapy is an essential treatment of premature infants suffering from hypoxemia. Normoxemia is maintained by an adjustment of the fraction of oxygen (FiO<sub>2</sub>) in the inhaled gas mixture that is set manually or automatically based on peripheral oxygen saturation (SpO<sub>2</sub>). Automatic closed-loop systems could be more successful in controlling SpO<sub>2</sub> than traditional manual approaches. Computer models of neonatal oxygen transport have been developed as a tool for design, validation, and comparison of the automatic control algorithms. The aim of this study was to investigate and implement the time delay of oxygen delivery after a change of set FiO<sub>2</sub> during noninvasive ventilation support to enhance an available mathematical model of neonatal oxygen transport. The time delay of oxygen delivery after the change of FiO<sub>2</sub> during the noninvasive nasal Continuous Positive Airway Pressure (nCPAP) ventilation support and during the High Flow High Humidity Nasal Cannula (HFHHNC) ventilation support was experimentally measured using an electromechanical gas blender and a physical model of neonatal lungs. Results show the overall time delay of the change in the oxygen fraction can be divided into the baseline of delay, with a typical time delay 5.5 s for nCPAP and 6.5 s for HFHHNC s, and an exponential rising phase with a time constant about 2–3 s. A delay subsystem was implemented into the mathematical model for a more realistic performance when simulating closed-loop control of oxygenation.</p>

Observation of dual-peak signal-to-noise ratios from plasmas produced in typical laser-induced breakdown spectroscopy (LIBS) experiments

In this work, emission properties of representative trace and major species in steel plasma plumes produced in typical laser-induced breakdown spectroscopy (LIBS) experiments under standard atmospheric conditions are investigated. The correlation between laser fluence and spatially integrated measurements of emission characteristics of the plasma at a typical delay time of 2 µs from the laser pulse onset is thoroughly explored. Q-switched neodymium-doped yttrium aluminum garnet (Nd: YAG) laser emitting at its fundamental wavelength of 1064 nm was employed to generate the plasmas under investigation. The results showed that the signal-to-noise ratio of all lines investigated exhibit irregular behaviour in which two maxima can be identified at specific laser fluence values. This behaviour is attributed to lower standard deviation of the background intensity indicating stable plasma conditions relevant for spectrochemical analysis. Plasma shielding of the incident laser energy, due to electron-atom inverse bremsstrahlung (IB), becomes more critical beyond laser fluencies larger than about 45 J cm-2.

SN1991bg-like supernovae are associated with old stellar populations

Abstract SN1991bg-like supernovae are a distinct subclass of thermonuclear Type Ia supernovae (SNe Ia). Their spectral and photometric peculiarities indicate that their progenitors and explosion mechanisms differ from ‘normal’ SNe Ia. One method of determining information about supernova progenitors we cannot directly observe is to observe the stellar population adjacent to the apparent supernova explosion site to infer the distribution of stellar population ages and metallicities. We obtain integral field observations and analyse the spectra extracted from regions of projected radius $\sim\,\text{kpc}$ about the apparent SN explosion site for 11 91bg-like SNe in both early- and late-type galaxies. We utilise full-spectrum spectral fitting to determine the ages and metallicities of the stellar population within the aperture. We find that the majority of the stellar populations that hosted 91bg-like supernovae have little recent star formation. The ages of the stellar populations suggest that that 91bg-like SN progenitors explode after delay times of >6 Gyr, much longer than the typical delay time of normal SNe Ia, which peaks at $\sim$ 1 Gyr.

High-accuracy optical time delay measurement in fiber link [Invited

Optoelectronic components and subsystems such as optically controlled phased array antennas, distributed radar networks, interferometric optical fiber hydrophones, and high-speed optoelectronic chips demand high-accuracy optical time delay measurement with large measurement range and the capability for single-end and wavelength-dependent measurement. In this paper, the recent advances in the optical time delay measurement of a fiber link with high accuracy are reviewed. The general models of the typical time delay measurement technologies are established with the operational principle analyzed. The performance of these techniques is also discussed.

Upgrade of the Time of Flight system of the CMD-3 detector

Upgrade of the Time of Flight (TOF) system of the CMD-3 detector is described. The TOF is located inside the narrow gap between two layers of the cylindrical calorimeter based on the liquid Xe and CsI crystals. The TOF system is made from thin plates of plastic scintillator and is intended for measuring the time of flight of particles through the detector, in particular to detect products of antineutron annihilations in the calorimeters. Due to low velocities of antineutrons, the average times of annihilation in the calorimeters have a typical delay time about 4–10 ns with respect to the beam collision.

Strongly lensed repeating fast radio bursts as precision probes of the universe

Fast radio bursts (FRBs), bright transients with millisecond durations at ∼GHz and typical redshifts probably >0.8, are likely to be gravitationally lensed by intervening galaxies. Since the time delay between images of strongly lensed FRB can be measured to extremely high precision because of the large ratio ∼109 between the typical galaxy-lensing delay time sim{cal O} (10 days) and the width of bursts sim{cal O} (ms), we propose strongly lensed FRBs as precision probes of the universe. We show that, within the flat ΛCDM model, the Hubble constant H0 can be constrained with a ~0.91% uncertainty from 10 such systems probably observed with the square kilometer array (SKA) in <30 years. More importantly, the cosmic curvature can be model independently constrained to a precision of ∼0.076. This constraint can directly test the validity of the cosmological principle and break the intractable degeneracy between the cosmic curvature and dark energy.

State‐dependent switching control of delayed switched systems with stable and unstable modes

In this paper, the problem of switching stabilization for a class of delayed switched systems is studied by using state‐dependent switching control. Some sufficient conditions for asymptotic stability of delayed switched systems are derived, which are based on the Lyapunov functional method. The derived stability conditions can be applied for delayed switched systems with partial or all unstable modes. Moreover, a typical time delay called leakage delay existing in the negative feedback term of a system are also considered. Two numerical examples, that is, a switched system with two unstable modes and a switched system with delayed feedback control, are given to show the effectiveness of the main results.

Does the Black Hole Merger Rate Evolve with Redshift?

Abstract We explore the ability of gravitational-wave detectors to extract the redshift distribution of binary black hole (BBH) mergers. The evolution of the merger rate across redshifts 0 &lt; z ≲ 1 is directly tied to the formation and evolutionary processes, providing insight regarding the progenitor formation rate together with the distribution of time delays between formation and merger. Because the limiting distance to which BBHs are detected depends on the masses of the binary, the redshift distribution of detected binaries depends on their underlying mass distribution. We therefore consider the mass and redshift distributions simultaneously, and fit the merger rate density, dN/dm 1 dm 2 dz. Our constraints on the mass distribution agree with previously published results, including evidence for an upper mass cutoff at ∼40 M ⊙. Additionally, we show that the current set of six BBH detections are consistent with a merger rate density that is uniform in comoving volume. Although our constraints on the redshift distribution are not yet tight enough to distinguish between BBH formation channels, we show that it will be possible to distinguish between different astrophysically motivated models of the merger rate evolution with ∼100–300 Laser Interferometer Gravitational-Wave Observatory/Virgo detections (to be expected within 2–5 years). Specifically, we will be able to infer whether the formation rate peaks at higher or lower redshifts than the star formation rate, or the typical time delay between formation and merger. Meanwhile, with ∼100 detections, the inferred redshift distribution will place constraints on more exotic scenarios such as modified gravity.