Transmission Time Delay Research Articles

Application of the TDFA window in true optical time delay systems.

Recent advances in silicon photonic components operating in the thulium-doped fiber amplifier (TDFA) wavelength regime around 2-µm have shown that these wavelengths hold great promise for on-chip photonic systems. Here we present our work on characterizing a Mach-Zehnder interferometer coupled silicon photonic ring resonator operating in the TDFA window for optical time delay applications. We describe the optical transmission and variable time delay properties of the resonator, including a detailed characterization and comparison of the directional coupler and Mach-Zehnder interferometer base components at both 1930 and 1550 nm wavelengths. The results show tuning of a ring from a 190-ps peak time delay at a resonant extinction ratio of 5.1-dB to a 560-ps peak time delay at an extinction ratio of 11.0-dB, in good agreement with optical models of the device. These results demonstrate significant promise towards the future application of TDFA band devices in optical time delay systems.

Group delay time of fermions in graphene through tilted potential barrier

The group delay time of Dirac fermions subjected to a tilting barrier potential along the $ x $-axis is investigated in graphene. We start by finding the eigenspinor solution of the Dirac equation and then relating it to incident, reflected, and transmitted beam waves. This relationship allows us to compute the group delay time in transmission and reflection by obtaining the corresponding phase shifts. We discovered that the barrier width, incident energy, and incident angle can all be used to modify the group delay time, and that the particles travel through the barrier at the Fermi velocity $ v_F $. Our findings also show that the transmission group delay might be controlled, and that gate voltage control could be useful in graphene-based tilting barriers.

Mechanical Compliance of Individual Fractures in a Heterogeneous Rock Mass From Production‐Type Full‐Waveform Sonic Data

AbstractThe mechanical fracture compliance is of interest in a number of geoscientific applications. Seismic borehole methods, especially full‐waveform sonic (FWS) data, have indicated their potential to infer the compliance of macroscopic fractures under in situ conditions. These approaches rely on the assumption of a homogeneous background embedding the fractures and, as of yet, compliance estimates for individual fractures are limited to static FWS measurements. In this work, we assess the potential of inferring the compliance of individual fractures from standard, production‐type FWS data in the presence of background heterogeneity. We first perform a comparative test on synthetic data to evaluate three approaches known as the transmission, phase, and group time delay methods. The results indicate that the former two produce adequate compliance estimates for scenarios with a strongly heterogeneous background or a damage zone around the fracture. These two methods are then applied to two FWS data sets acquired before and after a hydraulic stimulation campaign in a crystalline rock, which allows to test them on natural and man‐made fractures. The transmission method turned out to be unsuitable for the considered data due to its reliance on amplitudes. Conversely, the travel time behavior remained stable and the phase time delay method produced robust and consistent estimates. The results for a newly created hydro‐fracture imply the capability of resolving remarkably small compliance values of the order of 10−14 m/Pa. This estimate is one order‐of‐magnitude smaller than that for the natural fracture, which may help to distinguish between these two fracture types.

Robust Multi-Objective H2/H∞ Load Frequency Control of Multi-Area Interconnected Power Systems Using TS Fuzzy Modeling by Considering Delay and Uncertainty

The main objective of this paper is to design a robust multi-objective H2/H∞ delayed feedback controller for load frequency control of a multi-area interconnected power system by taking into account all theoretical and practical constraints. To achieve more precise modelling and analysis, the limitation of valve position, governor, and transmission delay are considered to guarantee of LFC system’s stability in practical applications. The nonlinear delayed system is approximated by the Takagi–Sugeno fuzzy model. Then, a parallel distributed compensation scheme is utilized for designing the control system of the overall system. The proposed multi-objective and robust H2/H∞ controller simultaneously minimizes the H2 and H∞ control performance indexes. Finally, simulation results verify the robustness and effectiveness of the proposed scheme in dealing with the impact of load disturbances, model uncertainties, transmission time delays, and nonlinearities in the model.

Reconstructing distant interactions of multiple paths between perceptible nodes in dark networks.

Quantitative research of interdisciplinary fields, including biological and social systems, has attracted great attention in recent years. Complex networks are popular and important tools for the investigations. Explosively increasing data are created by practical networks, from which useful information about dynamic networks can be extracted. From data to network structure, i.e., network reconstruction, is a crucial task. There are many difficulties in fulfilling network reconstruction, including data shortage (existence of hidden nodes) and time delay for signal propagation between adjacent nodes. In this paper a deep network reconstruction method is proposed, which can work in the conditions that even only two nodes (say A and B) are perceptible and all other network nodes are hidden. With a well-designed stochastic driving on node A, this method can reconstruct multiple interaction paths from A to B based on measured data. The distance, effective intensity, and transmission time delay of each path can be inferred accurately.

On the Simulation of Communication Protocols with Multiple Mobile Nodes

<p>In this paper, a high-performance routing protocol with multiple mobile nodes based on reliable active nodes is put forward since network nodes are not involved in the reliability work when the existing OSPF routing protocol forwards the packet, which results in several problems such as a low rate of packet forwarding, the long average delay of end-to-end, high energy consumption of network nodes and short service lifetime of nodes. The hierarchical model of active networks with multiple-mobile nodes was built, in which, reliable active nodes were divided into forwarding nodes and reliable nodes based on the functional requirements of this model, and consideration was given both to the efficiency and reliability of packet transmission. Besides, the energy consumption of network communication was calculated on the basis of this model and the packet transmission power was controlled. A high-performance routing protocol with multiple mobile nodes was designed to estimate the packet transmission delay time, calculate the forwarding moderate index of nodes, and select neighbor nodes in the active network. The simulation results show that this routing communication protocol effectively improves the packet forwarding rate, lowers the total energy consumption, shortens the average delay of end-to-end, and extends the service life of network nodes.</p> <p> </p>

A forest fire monitoring and detection system based on wireless sensor networks

Global climate change is affecting Earth in various ways, including glacial detachment, sea-level rise, and more intense heat waves, which in turn contribute to fires in areas rich in flora and fauna, causing erosion and changes in plant and animal ranges. Despite international efforts to mitigate climate change, the problem remains uncontrolled in many areas. In this study, a forest fire monitoring and early warning system is proposed. It is based on a wireless sensor network (WSN) that measures the environment to detect and prevent fires in rural areas. The WSN uses open-access technologies and the Zigbee standard for radiofrequency communication and sends collected data to a web server via GPRS and TCP/IP protocol. The WSN's performance is evaluated using two metrics: data transmission rate and time delay. The WSN achieved an average success rate of data transmission greater than 86% with an average time delay of less than 500 milliseconds in all tests, demonstrating the potential of WSNs as near real-time forest fire detection systems.

Tailoring temperature stability of MgAl2O4 microwave dielectric ceramic via (Cu0.5Ti0.5)3+ co-substituted

In this work, the MgAl2-x(Cu0.5Ti0.5)xO4 (x ​= ​0, 0.04, 0.08, 0.12, 0.16, and 0.20) ceramic system was synthesized using the solid-state route. The crystalline phases, crystal structure,and microwave dielectric properties of the samples were investigated. The XRD data presented a typical spinel structure of MgAl2O4 and was processed using the Rietveld refinement method. TiO2, Al2TiO5 and MgTi2O5 were considered as secondary phases. SEM indicated that the densification was affected by the (Cu0.5Ti0.5)3+ content and sintering temperature. The successful fabrication of MgAl2-x(Cu0.5Ti0.5)xO4 and the presence of MgTi2O5 were confirmed by EDS. The densification, secondary phases and cation vacancies were responsible for the variation of Qf values. The εr values were dominated by secondary phases and ionic polarizability. Meanwhile, secondary phases and bond valence had a significant influence on the τf values. The optimum microwave dielectric properties (Qf ​= ​42,036 ​GHz, εr ​= ​8.72 and τf ​= ​-5.0 ​ppm/°C) were obtained. Temperature stability was improved by 93.8% when compared to pure MgAl2O4 (τf ​= ​-80.0 ​ppm/°C). The as-prepared ceramics possess low transmission delay time, high temperature stability, preferable frequency selective characteristics, and low dielectric loss.

Use of transmission and reflection complex time delays to reveal scattering matrix poles and zeros: Example of the ring graph.

We identify the poles and zeros of the scattering matrix of a simple quantum graph by means of systematic measurement and analysis of Wigner, transmission, and reflection complex time delays. We examine the ring graph because it displays both shape and Feshbach resonances, the latter of which arises from an embedded eigenstate on the real frequency axis. Our analysis provides a unified understanding of the so-called shape, Feshbach, electromagnetically induced transparency, and Fano resonances on the basis of the distribution of poles and zeros of the scattering matrix in the complex frequency plane. It also provides a first-principles understanding of sharp resonant scattering features and associated large time delay in a variety of practical devices, including photonic microring resonators, microwave ring resonators, and mesoscopic ring-shaped conductor devices. Our analysis involves use of the reflection time difference, as well as a comprehensive use of complex time delay, to analyze experimental scattering data.

The frame synchronization robust to low signal power in underwater acoustic communications

In underwater acoustic communications, it is difficult to find the starting time of received signals because of noise, multipath, transmission time delay, and Doppler frequency. In this paper, we solve the problem by using 2-STEP frame synchronization in the receiver. The transmitted signal is modulated by using burst PSK. The frame is composed of preamble of PN code and random data. The 2-STEP frame synchronization consist of non-coherent correlation, sliding FFT, and coherent correlation. First, in the STEP 1, the non-coherent correlation and sliding FFT are simultaneously performed to obtain an approximate start time of a frame in time domain and a Doppler frequency in frequency domain. However, through the results of the marine experiments, we can see that it is difficult to guarantee the starting time point in STEP 1 when the received signal power is weak and there is high Doppler frequency. Therefore, in the STEP 2, we use the coherent correlation to get more accurate start time stably after compensating the Doppler frequency of FFT in STEP 1. Finally, we can assure that the performance of the proposed 2-STEP frame synchronization is robust to low power of received signal and high Doppler frequency through marine experiments.

Integration of rhythmic metabolome and transcriptome provides insights into the transmission of rhythmic fluctuations and temporal diversity of metabolism in rice.

Various aspects of the organisms adapt to cyclically changing environmental conditions via transcriptional regulation. However, the role of rhythmicity in altering the global aspects of metabolism is poorly characterized. Here, we subjected four rice (Oryza sativa) varieties to a range of metabolic profiles and RNA-seq to investigate the temporal relationships of rhythm between transcription and metabolism. More than 40% of the rhythmic genes and a quarter of metabolites conservatively oscillated across four rice accessions. Compared with the metabolome, the transcriptome was more strongly regulated by rhythm; however, the rhythm of metabolites had an obvious opposite trend between day and night. Through association analysis, the time delay of rhythmic transmission from the transcript to the metabolite level was ∼4 h under long-day conditions, although the transmission was nearly synchronous for carbohydrate and nucleotide metabolism. The rhythmic accumulation of metabolites maintained highly coordinated temporal relationships in the metabolic network, whereas the correlation of some rhythmic metabolites, such as branched-chain amino acids (BCAAs), was significantly different intervariety. We further demonstrated that the cumulative diversity of BCAAs was due to the differential expression of branched-chain aminotransferase 2 at dawn. Our research reveals the flexible pattern of rice metabolic rhythm existing with conservation and diversity.

Robust Speed Tracking Control for Future Electric Vehicles under Network-Induced Delay and Road Slope Variation.

Integrated motor-transmission (IMT) powertrain systems are widely used in future electric vehicles due to the advantages of their simple structure configuration and high controllability. In electric vehicles, precise speed tracking control is critical to ensure good gear shifting quality of an IMT powertrain system. However, the speed tracking control design becomes challenging due to the inevitable time delay of signal transmission introduced by the in-vehicle network and unknown road slope variation. Moreover, the system parameter uncertainties and signal measurement noise also increase the difficulty for the control algorithm. To address these issues, in this paper a robust speed tracking control strategy for electric vehicles with an IMT powertrain system is proposed. A disturbance observer and low-pass filter are developed to decrease the side effect from the unknown road slope variation and measurement noise and reduce the estimation error of the external load torque. Then, the network-induced delay speed tracking model is developed and is upgraded considering the damping coefficient uncertainties of the IMT powertrain system, which can be described through the norm-bounded uncertainty reduction method. To handle the network-induced delay and parameter uncertainties, a novel and less-conservative Lyapunov function is proposed to design the robust speed tracking controller by the linear matrix inequality (LMI) algorithm. Meanwhile, the estimation error and measurement noise are considered as the external disturbances in the controller design to promote robustness. Finally, the results demonstrate that the proposed controller has the advantages of strong robustness, excellent speed tracking performance, and ride comfort over the current existing controllers.

The influence of autapse on synchronous firing in small-world neural networks

The synchronization of the nervous system is strongly related to diseases such as Parkinson’s, epilepsy, and schizophrenia. Given that the existence of autapse has been proved experimentally, the influence of autapse on the synchronization in a neural network is studied numerically. The results show that increasing coupling intensity could destroy the synchronization of the neural firing pattern, and reduce the firing rate in the network. Especially, an inhibition zone, in which the neural firing is inhibited completely, exists for changes of both coupling intensity and time delay in all types of autapses. As a key factor for different types of autapses, the transmission time delay influences the synchronization complicatedly, i.e., increasing time delay could modulate synchronization for different types of autapse and parameter regions. The theoretical results in this paper shed some light on the study about the mechanism of neural synchronization.

Asymmetry of EPR signal response in nuclear magnetic resonance gyroscope

The spin relaxation time of alkali atoms in nuclear magnetic resonance gyroscope is usually on the order of 10<sup>–5</sup> s, which is much less than that in atomic magnetometers. The response of electron paramagnetic resonance signals of atoms with short relaxation time is asymmetric in different directions under oscillating magnetic fields, which makes the measurement results of atomic transverse relaxation time and Larmor frequency different. In this work this phenomenon is analyzed based on Bloch equation theory and the theoretical correction is given. The shorter the relaxation time, the greater the differences of the response intensity and resonance frequency of the electron paramagnetic resonance signal under different magnetic field directions will be. Using this property, the transmission delay time of the system can be measured accurately. In this paper proposed is a method of measuring transverse relaxation time based on the difference between signal phases in <i>X</i>-axis direction and <i>Y</i><italic/>-axis direction, which can accurately and quickly measure very short transverse relaxation time. The difference between the half-width fitting method and the phase measurement method is compared by measuring the transverse relaxation times of <sup>87</sup>Rb atoms under different magnetic field intensities. The half-width fitting method is greatly affected by the transmission delay time and has its measurement limit. The phase measurement method is greatly affected by the angle of the probe light, but the measurement range is wider and the anti-magnetic interference ability is stronger.

Consensus-Based Distributed Estimation in the Presence of Heterogeneous, Time-Invariant Delays

Classical distributed estimation scenarios typically assume timely and reliable exchanges of information over the sensor network. This letter, in contrast, considers single time-scale distributed estimation via a sensor network subject to transmission time-delays. The proposed discrete-time networked estimator consists of two steps: (i) consensus on (delayed) a-priori estimates, and (ii) measurement update. The sensors only share their a-priori estimates with their out-neighbors over (possibly) time-delayed transmission links. The delays are assumed to be fixed over time, heterogeneous, and known. We assume distributed observability instead of local observability, which significantly reduces the communication/sensing loads on sensors. Using the notions of augmented matrices and the Kronecker product, the convergence of the proposed estimator over strongly-connected networks is proved for a specific upper-bound on the time-delay.

Large-Scale 3D Baseline Measurement Based on Phase-Stabilized GNSS-Over-Fiber System

Multi-antenna GNSS-over-fiber system is considered an effective solution for three-dimension (3D) baseline measurement. By precisely determining the transmission time delays between the antennas and the receiver, the vertical precision can be improved based on the single difference (SD) model. This method, however, would encounter problems if the baseline is too long, since a high precision measurement of the time delay of a long fiber link is usually time-consuming. Here, we propose and demonstrate a high-speed phase-stabilized GNSS-over-fiber system for large-scale 3D baseline measurement. A relatively slow but accurate time delay measurement module is used to calibrate the link delay, then a fast active compensation device is employed to keep the time delay constant. If the delay variation exceeds the compensation range, the time delay measurement module would measure the link delay again and bias the active compensation device at a new operating state. In a proof-of-concept experiment, the precision of the 3D baseline measurement obtained by the proposed system with a 20-km optical fiber is around 2.82 mm thanks to the rigid active compensation and the high-precision time delay measurement. If the active compensation device is disabled, the vertical precision of the baseline measurement obtained would be degraded from 2.82 mm to 16.46 mm in 10 minutes.

Wave propagation in a diffusive SEIR epidemic model with nonlocal transmission and a general nonlinear incidence rate

We introduce a diffusive SEIR model with nonlocal delayed transmission between the infected subpopulation and the susceptible subpopulation with a general nonlinear incidence. We show that our results on existence and nonexistence of traveling wave solutions are determined by the basic reproduction number R_{0}=partial _{I}F(S_{0},0)/gamma of the corresponding ordinary differential equations and the minimal wave speed c^{*}. The main difficulties lie in the fact that the semiflow generated here does not admit the order-preserving property. In the present paper, we overcome these difficulties to obtain the threshold dynamics. In view of the numerical simulations, we also obtain that the minimal wave speed is explicitly determined by the time delay and nonlocality in disease transmission and by the spatial movement pattern of the exposed and infected individuals.

Computer simulation of the dynamics of a spatial susceptible-infected-recovered epidemic model with time delays in transmission and treatment

Background and objective: In this work, we analyze the spatial-temporal dynamics of a susceptible-infected-recovered (SIR) epidemic model with time delays. To better describe the dynamical behavior of the model, we take into account the cumulative effects of diffusion in the population dynamics, and the time delays in both the Holling type II treatment and the disease transmission process, respectively. Methods: We perform linear stability analyses on the disease-free and endemic equilibria. We provide the expression of the basic reproduction number and set conditions on the backward bifurcation using Castillo’s theorem. The values of the critical time transmission, the treatment delays and the relationship between them are established. Results: We show that the treatment rate decreases the basic reproduction number while the transmission rate significantly affects the bifurcation process in the system. The transmission and treatment time-delays are found to be inversely proportional to the susceptible and infected diffusion rates. The analytical results are numerically tested. The results show that the treatment rate significantly reduces the density of infected population and ensures the transition from the unstable to the stable domain. Moreover, the system is more sensible to the treatment in the stable domain. Conclusions: The density of infected population increases with respect to the infected and susceptible diffusion rates. Both effects of treatment and transmission delays significantly affect the behavior of the system. The transmission time-delay at the critical point ensures the transition from the stable (low density) to the unstable (high density) domain.

Optimal Allocation of Vaccine and Antiviral Drugs for Influenza Containment over Delayed Multiscale Epidemic Model considering Time-Dependent Transmission Rate.

In this study, two types of epidemiological models called “within host” and “between hosts” have been studied. The within-host model represents the innate immune response, and the between-hosts model signifies the SEIR (susceptible, exposed, infected, and recovered) epidemic model. The major contribution of this paper is to break the chain of infectious disease transmission by reducing the number of susceptible and infected people via transferring them to the recovered people group with vaccination and antiviral treatment, respectively. Both transfers are considered with time delay. In the first step, optimal control theory is applied to calculate the optimal final time to control the disease within a host's body with a cost function. To this end, the vaccination that represents the effort that converts healthy cells into resistant-to-infection cells in the susceptible individual's body is used as the first control input to vaccinate the susceptible individual against the disease. Moreover, the next control input (antiviral treatment) is applied to eradicate the concentrations of the virus and convert healthy cells into resistant-to-infection cells simultaneously in the infected person's body to treat the infected individual. The calculated optimal time in the first step is considered as the delay of vaccination and antiviral treatment in the SEIR dynamic model. Using Pontryagin's maximum principle in the second step, an optimal control strategy is also applied to an SEIR mathematical model with a nonlinear transmission rate and time delay, which is computed as optimal time in the first step. Numerical results are consistent with the analytical ones and corroborate our theoretical results.

Gap-tunable of tunneling time in graphene magnetic barrier

We study the tunneling time of Dirac fermions in graphene magnetic barrier through an electrostatic potential and a mass term. This latter generates an energy gap in the spectrum and therefore affects the proprieties of tunneling of the system. For clarification, we first start by deriving the eigenspinors solutions of Dirac equation and second connect them to the incident, reflected and transmitted beam waves. This connection allows us to obtain the corresponding phases shifts and consequently compute the group delay time in transmission and reflection. Our numerical results show that the group delay time depends strongly on the energy gap in the tunneling process through single barrier. Moreover, we find that the group approaches unity at some critical value of the energy gap and becomes independent to the strengths of involved physical parameters.