Maximum Time Delay Research Articles

Dynamic connectivity maintenance problems in networks of multi‐agent systems via nearest neighbor‐based methods

AbstractConnectivity maintenance is crucial for the real‐world deployment of multi‐agent systems, as it ultimately allows the agents to communicate, coordinate, and perform tasks in a collaborative way. In this paper, a new problem called the dynamic connectivity maintenance problem is considered, which aims to model the scenario where part agents have already broken away from the original communication range but still could be communicated by the other agents. To this end, nearest neighbor‐based methods are proposed in this paper to ensure that the graphs of multi‐agent systems have a spanning tree at all times. Considering that it takes time during the dynamic connectivity maintenance process, this paper also considers the impact of non‐uniform time‐varying time delays on communication and obtains a solution to the gain under the maximum time delay through the Lyapunov method when achieving a consensus. A new approach based on a chain‐type transformation to investigate the consensus problem is proposed. Some sufficient conditions are established. Finally, the developed approaches are validated through a simulation of unmanned surface vessels and a task of autonomous driving truck fleet.

C-SPPO: A deep reinforcement learning framework for large-scale dynamic logistics UAV routing problem

Unmanned Aerial Vehicle (UAV) stands as a burgeoning electric transportation carrier, holding substantial promise for the logistics sector. A reinforcement learning framework Centralized - S Proximal Policy Optimization (C-SPPO) based on centralized decision process and considering policy entropy (S) is proposed. The proposed framework aims to plan the best scheduling scheme with the objective of minimizing both the timeout of order requests and the flight impact of UAVs that may lead to conflicts. In this framework, the intents of matching act are generated through the observations of UAV agents, and the ultimate conflict-free matching results are output under the guidance of a centralized decision maker. Concurrently, a pre-activation operation is introduced to further enhance the cooperation among UAV agents. Simulation experiments based on real-world data from New York City are conducted. The results indicate that the proposed C-SPPO outperforms the baseline algorithms in the Average Delay Time (ADT), the Maximum Delay Time (MDT), the Order Delay Rate (ODR), the Average Flight Distance (AFD), and the Flight Impact Ratio (FIR). Furthermore, the framework demonstrates scalability to scenarios of different sizes without requiring additional training.

Adjustable slow light with high group index in a graphene metasurface based on plasmon-induced transparency

A relatively simple metasurface structure is proposed to achieve a dynamically tunable slow light effect. The metasurface consists of two horizontal graphene strips and two vertical continuous graphene strips. Strong interference between the bright and dark modes enables the metasurface to generate a significant triple plasmon-induced transparency (PIT). Varying the coupling distance between the horizontal strips, double-PIT and triple-PIT can be transformed into each other. During the reduction of the transparent window, electromagnetic waves undergo strong phase changes, resulting in a higher group index. After structural optimization, the maximum time delay and group index can be as high as 2.624 ps and 3934, surpassing comparable slow light devices. The proposed patterned graphene metasurface provides theoretical guidance for designing high-performance slow light devices for optical storage, nonlinear optics and quantum optics.

Rapid-calibration optical tunable delay line on 3-µm-thick SOI photonic platforms.

Optical tunable delay lines (OTDLs) which can capture temporal optical signals, and overcome the challenge of halting light are crucial for optical communications and microwave photonics. Here, a rapid-calibration 8-bit OTDL on the 3-µm-thick silicon-on-insulator (SOI) platform consisting of waveguide spirals and integrated optical switches is proposed, achieving a maximum delay time of 3570 ps with a resolution of 14 ps/stage. The large delay is attributed to the spirals of a 3-µm-thick SOI platform featuring a delay efficiency of approximately 11.49 ps/mm, with wavelength-insensitivity transmission loss of 0.32 dB/cm, and the polarization-dependent loss is only 0.075 dB/cm within 140 nm bandwidth. In addition, the optical switches with extinction ratios up to 50 dB. Integrated variable optical attenuators can suppress crosstalk and facilitate rapid calibration for OTDLs. The advantages of OTDLs' large delay time, high signal-to-noise, and rapid calibration make them suitable for optical programmers and microwave photonics radars.

Strength development and durability requirement in recycled aggregate concrete: effect of drying and post curing

Present research critically investigates drying sensitivity and cement hydration resumption in recycled aggregate concrete (RAC). To determine minimum post-curing time for optimum strength resumption in RAC, a curing ratio (δ) is introduced. Curing ratio is defined as the ratio between post-curing duration and delay time before curing. Drying sensitivity of RAC is observed significantly lower than NAC. The maximum strength loss under drying conditions is 25.9% in RAC (OPC) and 23.2% in RAC (PPC). Strength criteria determine the curing ratios of RAC (OPC) and RAC (PPC) as 2.22 and 0.30. The maximum delay time for RAC (OPC) and RAC (PPC) is determined at 8 days and 21 days with a minimum post-curing for 17.76 and 6.63 days. The longest allowable delay produces ion penetration less than 1000 Coulombs, resistivity greater than 208 ohm-m, superior structural integrity and internal compactness, and sorptivity comparable to RACs cured after a shorter delay.

Research on Edge Cloud Data Storage Method of Power Operation Site in Internet of Things Environment Based on Paxos Algorithm

Abstract In order to realize the efficient storage of electric power job site data and ensure the utilization effect of the stored data, a method of electric power job site edge cloud data storage based on the Paxos algorithm is proposed. In this method, power field operation data are collected comprehensively through the edge server and edge controller in the edge computing module, the collected data are processed, and the data storage tasks are allocated reasonably. The allocated data are transferred to the data storage module, which identifies the bad data in the data through a gap statistics algorithm and cluster analysis and retains the valid and normal data. After the primary and secondary nodes are determined based on the Paxos algorithm, the data storage model of power operation site is constructed. After the consistency detection of the reserved data, the data storage of power operation site is completed. The platform management module can analyze the stored data and present the analysis results to the application decision-making module for presentation. The test results show that the maximum time delay and energy consumption are 2.15 s and 42.6 W, respectively, when the method is used for data transmission, which can accurately identify the bad data in the field data of electric power operation, and the reliability index results of data consistency detection are all above 0.95, which ensures the good consistency of the stored power operation site data and effectively completes the power operation site data storage.

Flexible optimal bus‐schedule bridging for metro operation‐interruption

AbstractUnder the sudden interruption of the metro, it is significant to dispatch emergency bridging buses to evacuate stranded passengers to improve linkage management and service reliability. Aiming at the problem of emergency bridging bus scheduling, considering the remaining capacity of conventional buses, passenger tolerance, and site convenience, a flexible combined emergency bridging bus scheduling model is constructed based on the constraints of vehicle capacity, dispatching capacity, and maximum evacuation times of emergency bridging bus, aiming at minimizing the maximum evacuation time and passenger delay. The improved Harris hawk algorithm is used to solve the model, and the evacuation plan of the demand‐responsive and station‐station bridging lines is obtained. The maximum evacuation time is 41 min, and the average delay of stranded passengers is 19 min. The results show that the maximum evacuation time is 10% and 27% less than the fixed combined and single scheduling. The average delay is 16% and 42% less than the fixed combination and traditional single scheduling. The sensitivity analysis of the influencing factors of emergency bridging bus scheduling is conducted. The results show that the flexible combined emergency bridging bus scheduling model constructed in this paper can improve evacuation efficiency and reduce passenger travel delays.

Concrete ablation depth analysis of OPR1000 NPP during top flooding ex-vessel cooling

This study assesses the integrity of OPR1000 nuclear power plant (NPP) containment during top flooding ex-vessel cooling in the event of a postulated severe accident. Maintaining containment integrity during ex-vessel cooling is critical for preventing substantial release of radioactive materials to the environment. To analyze the feasibility of top flooding ex-vessel cooling of the OPR1000 NPP, the spread of molten corium in the dry reactor cavity is first calculated, followed by calculating the concrete ablation depth according to the reactor cavity flooding delay time. It is judged whether the leak-tightness integrity of the containment during ex-vessel cooling is maintained based on whether the containment liner plate (CLP) is damaged or not. In the first step analysis, the spread of molten corium in the dry reactor cavity is calculated using computational fluid dynamics (CFD) methodology for various cases, and results indicate a uniform deposition of approximately 143 tonnes of molten corium, with a thickness of about 33 cm, meaning that the thermal load is distributed uniformly in the reactor cavity. In the second step analysis, concrete ablation depths are calculated base on the delay time for flooding the reactor cavity. For the postulated severe accident, injecting coolant into the reactor cavity one hour after breach of the reactor vessel results in a concrete ablation depth of about 0.74 m, indicating no damage to the CLP and ensuring containment integrity. The maximum allowable delay time for flooding the reactor cavity for the postulated severe accident is evaluated to be 2.24 hours maintaining the leak-tightness integrity of the OPR1000 NPP containment. The research methodology and findings presented in this study are expected to aid in assessing the feasibility of top flooding ex-vessel cooling and establishing appropriate accident management strategies for nuclear power plants like the OPR1000 NPP.

Learning-based asynchronous sliding mode control for semi-Markov jump systems with time-varying delay using relaxed negative-determination lemma

This article figures out the asynchronous sliding mode control (SMC) issue for a class of semi-Markov jump systems (SMJSs) with time-varying delay and actuator faults. Firstly, to tackle the chattering produced by asynchronous phenomenon and guarantee smooth reachability, the hidden Markov model and the reduced-order theory are used to design the learning-based SMC law. Besides, the mode-dependent augmented Lyapunov–Krasovskii functional (LKF) is constructed. By using the relaxed negative definite lemma and the generalized free matrix integral inequality (GFMBII), sufficient conditions for ensuring the stochastic stability of the SMJSs are provided. Furthermore, the conservatism of the maximum time delay is effectively reduced by adjusting the value of β. Finally, simulation examples prove the validity and superiority of the proposed method.

Asynchronous sampled-data control for connected vehicles with heterogeneous delays

This study investigates an asynchronous sampled-data control problem of vehicular platoons, with heterogeneous sampling, subjected to actuator delays. Without a synchronized clock, a completely asynchronous sampled-data controller is designed for each follower, where the state of the ith follower itself and its neighboring vehicles are sampled at their own sampling time instants. The caused closed-loop tracking error dynamics for the entire platoon considering the effect of the nonuniform sampling time intervals, heterogeneous vehicle dynamics, inter-vehicle topology and heterogeneous time delays. To simplify the stability analysis and controller design, the tracking-error dynamics of the entire platoon are decomposed into individual subsystems with reduced-order dynamics. Based on Lyapunov stability theory, the optimal conditions are explored to design an asynchronous sampled-data controller to guarantee the desired stability performance. Moreover, the exact values for the maximum allowable sampling interval and time delay are calculated for each follower using the designed feedback controller gain. The proposed asynchronous sampled-data control method is extended to a vehicular platoon using an event-based sampling scheme. Numerical examples are used to verify the effectiveness of the proposed sampled-data control method.

A carbon nanotube metamaterial sensor showing slow light properties based on double plasmon-induced transparency.

In this study, we proposed a bifunctional sensor of high sensitivity and slow light based on carbon nanotubes (CNTs). An array of left semicircular ring (LSR), right semicircular ring (RSR), and circular ring (CR) resonators are utilized to form the proposed metamaterial. The proposed structure can achieve double plasmon-induced transparency (PIT) effects under the excitation of a TM-polarization wave. The double PIT originated from the destructive interference between two bright modes and a dark mode. A coupled harmonic oscillator model is used to describe the destructive interference between the two bright modes and a dark mode, and the simulation results agree well with the calculated results. Moreover, we investigate the influence of the coupling distance, period, and flare angle on the PIT spectra. The relationship between the resonant frequencies, full width at half maximum (FWHM), amplitudes, quality factors (Q), and the coupling distance is also studied. Finally, a high sensitivity of 1.02 THz RIU-1 is obtained, and the transmission performance can be maintained at a good level when the incident angle is less than 40°. Thus, the sensor can cope with situations where electromagnetic waves are not perpendicular to the structure's surface. The maximum figure of merit (FOM) can reach about 8.26 RIU-1; to verify the slow light property of the device, the slow light performance of the proposed structure is investigated, and a maximum time delay (TD) of 22.26 ps is obtained. The proposed CNT-based metamaterial can be used in electromagnetically induced transparency applications, such as sensors, optical memory devices, and flexible terahertz functional devices.

Fractional-Order Sliding Mode Load Frequency Control and Stability Analysis for Interconnected Power Systems With Time-Varying Delay

The universal use of open communication networks in interconnected power systems has changed the constant delay in the formerly dedicated channels into time-varying delay. The delay will deteriorate the dynamic performance of the load frequency control and lead to system frequency instability. This paper presents a fractional-order sliding mode controller for interconnected power systems with time-varying delay and performs stability analysis based on the Lyapunov direct method. Firstly, fractional-order integral sliding mode control is used to improve the stability of interconnected power systems containing time-varying delay. This expands the delay margin by taking advantage of the scalability of the fractional-order to the sliding mode surface. Then, the Riemann-Liouville fractional-order Lyapunov functional is introduced to stability analysis. This reduced the conservatism of the stability analysis by adjusting the upper limit of the functional integral. Lastly, combining Lyapunov's theory and integral inequality to obtain the stability conditions of the time-varying delay power system described by linear matrix inequality, and bring the stability margin of the system. The simulation results show that the designed controller can guarantee that the maximum delay time of the system is less than a predefined upper limit. The proposed control strategy obtains a larger stability margin than the other four scenarios. Additional simulation study was also conducted to verify its robustness to load variations and wind fluctuations.

Ultra-compact optical full-adder based on directed logic and microring resonators.

Photonic integrated circuits with compact design have opened possibilities for the development of optical computing systems; however, the overuse of photonic components in optical designs has slowed the progress of dense integration. In this paper, we propose an ultra-compact optical full-adder based on directed logic and microring resonators. To the best of our knowledge, the proposed structure requires fewer optical components than any other current designs, resulting in a significantly reduced footprint 59.2µm×29.2µm. Also, the proposed structure exhibits a maximum delay time of approximately 10ps, implying a minimum date rate of 100GHz. Simulation results by finite-difference time-domain (FDTD) demonstrate the effectiveness and feasibility of the proposed optical full-adder.

Slowdown of group velocity of light in dual 1480 nm hybrid pump cascade structure of Er3+-doped optical fiber at room temperature

In this paper, a general theory of slow light transmission in dual 1480nm hybrid pump cascade structure of Er3+-doped optical fiber at room temperature is presented. Our objective is to compare the dual 1480nm hybrid pump cascade structure with the 1480nm and 980nm hybrid pump cascade structure in relative modulation attenuation, time delay, fractional delay, group velocity, refractive index, and signal optical loss. Through theoretical calculation, the maximum time delay is increased by 1.111 times and 1.162 times, and the maximum fractional delay is increased by 1.091 times and 1.132 times when the pump power ratio M=0.5 and 0.75. The loss coefficient is reduced to 0.1 when M=1. The results show that compared with the previous research methods, the dual 1480nm hybrid pump cascade structure can obtain larger time delay, fractional delay and smaller loss, which may have important applications for the optimization of optical communication systems.

Robust design and best control channel selection of FACTs-based WADC for improving power system stability using Grey Wolf Optimizer

With recent advances in wide-area measurement systems (WAMS), wide-area damping controllers (WADCs) based on remote signals can effectively damp inter-area oscillations. However, these signals are inherently subjected to communication time-delay which may adversely affect the damping of inter area oscillations. The purpose of this paper is to present a optimization-based method for designing a WADC for a static synchronous series compensator (SSSC) to improve the damping of inter-area oscillations by considering the time delays of remote control signals. For this aim, the control gain value of the WADC, shifting of the critical modes to a desirable area, and the maximum time delay margins are simultaneously considered as an objective function. Moreover, to design a WADC as minimum-phase structure, the suitable constraints have been determined and added to the objective function as penalty factors. A grey wolf optimization (GWO) algorithm is utilized to solve the optimization problem. Robustness of the designed SSSC-based WADC in amplitude and phase control channels against the time delay has been compared and then the best control channels to damp inter-area oscillations has been selected. Based on simulations and statistical results conducted on 4 and 50 machine multi-machine power systems, it is evident that the proposed method based on the GWO outperforms other techniques in achieving the optimal design of a SSSC-based WADC for damping inter-area oscillations.

Sensitivity of atom based on slow light propagation and rotary photon drag: an efficient and secure model for quantum-based sensors in Internet of Things

Quantum technology has the potential to revolutionize sensors and the Internet of Things (IoT). Efficient and secure data transfer among sensors and IoT devices is a major challenge. To address this, the manuscript presents coherent manipulation of the scattering cross section and its sensitivity based on subluminal propagation and rotary photon drag, using an atomic medium with two levels coupled with a cavity. The group index of the proposed atomic medium is measured in the range of -0.1le n_gle 150 and group velocity in the range of 2times 10^6m/sle v_gle pm 2times 10^9m/s. The maximum delay time is reported to t_g=0.3mu s and rotary photon drag to theta _d=pm 5 micro radian. This effect of photon drag is used in sensing, energy harvesting, and optical switching in IoT. The scattering cross-section of 0.1times 10^{21}m^2 is reported. The scattering cross-section impacts the efficiency and reliability of quantum-based communication for IoT. The maximum cross-sectional sensitivity is measured to S_sigma =0.4times 10^{-19}m^2/n_r. The cross-sectional sensitivity potentially impacts secure communication and highly precise detection in sensors and IoT.

Choroid plexus vascular reactivity in moyamoya: Implications for choroid plexus regulation in ischemic stress.

Choroid plexus (ChP) hyperemia has been observed in patients with intracranial vasculopathy and to reduce following successful surgical revascularization. This observation may be attributable to impaired vascular reserve of the ChP or other factors, such as the ChP responding to circulating markers of stress. We extend this work to test the hypothesis that vascular reserve of the ChP is unrelated to intracranial vasculopathy. We performed hypercapnic reactivity (blood oxygenation level-dependent; echo time=35ms; spatial resolution=3.5×3.5×3.5mm, repetition time=2000ms) and catheter angiography assessments of ChP reserve capacity and vascular patency in moyamoya patients (n=53) with and without prior surgical revascularization. Time regression analyses quantified maximum cerebrovascular reactivity and reactivity delay time in ChP and cortical flow territories of major intracranial vessels with steno-occlusion graded as <70%, 70%-99%, and occlusion using Warfarin-Aspirin-Symptomatic-Intracranial-Disease stenosis grading criteria. Analysis of variance (significance: two-sided Bonferroni-corrected p<.05) was applied to evaluate cortical and ChP reactivity, after accounting for end-tidal carbon dioxide change, for differing vasculopathy categories. In patients without prior revascularization, arterial vasculopathy was associated with reduced cortical reactivity and lengthened reactivity delay (p≤.01), as expected. Regardless of surgical history, the ChP reactivity metrics were not significantly related to the degree of proximal stenosis, consistent with ChP reactivity being largely preserved in this population. Findings are consistent with ChP reactivity in moyamoya not being dependent on observed vasculopathy. Future work may investigate the extent to which ChP hyperemia in chronic ischemia reflects circulating markers of glial or ischemic stress.

Inertial Measurement Unit-Based Real-Time Adaptive Algorithm for Human Walking Pattern and Gait Event Detection

In this work, a lightweight adaptive hybrid gait detection method with two inertial measurement units (IMUs) on the foot and thigh was developed and preliminarily evaluated. An adaptive detection algorithm is used to eliminate the pre-training phase and to modify parameters according to the changes within a walking trial using an adaptive two-level architecture. The present algorithm has a two-layer structure: a real-time detection algorithm for detecting the current gait pattern and events at 100 Hz., and a short-time online training layer for updating the parameters of gait models for each gait pattern. Three typical walking patterns, including level-ground walking (LGW), stair ascent (SA), and stair descent (SD), and four events/sub-phases of each pattern, can be detected on a portable Raspberry-Pi platform with two IMUs on the thigh and foot in real-time. A preliminary algorithm test was implemented with healthy subjects in common indoor corridors and stairs. The results showed that the on-board model training and event decoding processes took 20 ms and 1 ms, respectively. Motion detection accuracy was 97.8% for LGW, 95.6% for SA, and 97.1% for SD. F1-scores for event detection were over 0.86, and the maximum time delay was steadily below 51 ± 32.4 ms. Some of the events in gait models of SA and SD seemed to be correlated with knee extension and flexion. Given the simple and convenient hardware requirements, this method is suitable for knee assistive device applications.

Presenting a mathematical model for reduction of delays in construction projects considering quality management criteria in uncertainty conditions

Nowadays, organizations and corporations are fully aware of the fact that they can't satisfy their customers' needs considering the rapid change of their needs and tastes. In addition, the attempts made by organizations to add variety to their products and improving their own status don’t seem to be sufficient to meet customers' needs. Orientation of organizations and corporations to benefit from each other's expertise and facilities for satisfaction of customers'' needs in the form of a coherent and efficient supply chain was a strategy which has been the mere result of increasing technology growth. Therefore, Chance-Constrained Programming approach has been used in this study to compensate for the uncertainties resulting from construction projects. Therefore, after defining uncertainty-related parameters, such parameters will be included in the optimization model. The mathematical model provided in this study was multi-objective and multi-modal. In other words, different modes and conditions have been assumed for any activity. Moreover, one of the objectives assumed for mathematical model was to minimize the maximum delay time in project implementation. Then, GAMS software has been used to solve the mathematical model in small and medium scale and Matlab and NSGA-II meta-heuristic algorithm have been used to solve the model in large scale.

A Wideband True Time Delay Circuit Using 0.25 µm GaN HEMT Technology.

This paper presents a wideband 4-bit true time delay IC using a 0.25 μm GaN HEMT (High-Electron-Mobility Transistor) process for the beam-squint-free phased array antennas. The true time delay IC is implemented with a switched path circuit topology using DPDT (Double Pole Double Throw) with no shunt transistor in the inter-stages to improve the bandwidth and SPDT (Single Pole Single Throw) switches at the input and the output ports. The delay lines are implemented with CLC π-networks with the lumped element to ensure a compact chip size. A negative voltage generator and an SPI controller are implemented in the PCB (Printed Circuit Board) due to the lack of digital control logic in GaN technology. A maximum time delay of ~182 ps with a time delay resolution of 10.5 ps is achieved at DC-6 GHz. The RMS (Root Mean Square) time delay and amplitude error are <5 ps and <0.6 dB, respectively. The measured insertion loss is <6.8 dB and the input and output return losses are >10 dB at DC-6 GHz. The current consumption is nearly zero with a 3.3 V supply. The chip size including pads is 2.45 × 1.75 mm2. To the authors' knowledge, this is the first demonstration of a true time delay IC using GaN HEMT technology.