Optimal Delay Research Articles

Selection of Embedding Dimension and Delay Time in Phase Space Reconstruction via Symbolic Dynamics.

The modeling and prediction of chaotic time series require proper reconstruction of the state space from the available data in order to successfully estimate invariant properties of the embedded attractor. Thus, one must choose appropriate time delay and embedding dimension p for phase space reconstruction. The value of can be estimated from the Mutual Information, but this method is rather cumbersome computationally. Additionally, some researchers have recommended that should be chosen to be dependent on the embedding dimension p by means of an appropriate value for the time delay , which is the optimal time delay for independence of the time series. The C-C method, based on Correlation Integral, is a method simpler than Mutual Information and has been proposed to select optimally and . In this paper, we suggest a simple method for estimating and based on symbolic analysis and symbolic entropy. As in the C-C method, is estimated as the first local optimal time delay and as the time delay for independence of the time series. The method is applied to several chaotic time series that are the base of comparison for several techniques. The numerical simulations for these systems verify that the proposed symbolic-based method is useful for practitioners and, according to the studied models, has a better performance than the C-C method for the choice of the time delay and embedding dimension. In addition, the method is applied to EEG data in order to study and compare some dynamic characteristics of brain activity under epileptic episodes

An Efficient Approach for Big Data Aggregation Mechanism in Heterogeneous Wireless Connected Sensor Networks

Recently and due to the impressive growth in the amounts of transmitted data over the heterogeneous sensor networks and the emerged related technologies especially the Internet of Things in which the number of the connected devices and the data consumption are remarkably growing, big data has emerged as a widely recognized trend and is increasingly being talked about. The term big data is not only about the volume of data, but also refers to the high speed of transmission and the wide variety of information that is difficult to collect, store and process using the available classical technologies. Although the generated data by the individual sensors may not appear to be significant, all the data generated through the many sensors in the connected sensor networks are able to produce large volumes of data. Big data management imposes additional constraints on the wireless sensor networks and especially on the data aggregation process, which represents one of the essential paradigms in wireless sensor networks. Data aggregation process can represent a solution to the problem of big data by allowing data from different sources to be combined to eliminate the redundant ones and consequently reduce the amounts of data and the consumption of the available resources in the network. The main objective of this work is to propose a new approach for supporting big data in the data aggregation process in heterogeneous wireless sensor networks. The proposed approach aims to reduce the data aggregation cost in terms of energy consumption by balancing the data loads on the heterogeneous nodes. The proposal is improved by integrating the feedback control closed loop to reinforce the balance of the data aggregation load on the nodes, maintaining therefore an optimal delay and aggregation time.

The synthesis of white-laser source based on the frequency conversion with the Stark-chirped rapid adiabatic passage

In this paper, an efficient cascaded sum frequency generation (SFG) model based on Stark-chirped rapid adiabatic passage is established, in which the laser of signal, intermediate, and output corresponds to three primary, and an approach of white laser source synthesis is proposed. The research results show that the energy of the red laser can be almost converted into blue laser, while the green laser intensity is extremely low in the cascade SFG process. The farther away from the optimal coupling delay parameters, the smaller the corresponding conversion efficiency is. Meanwhile, the pump intensity has a larger control range for conversion efficiency. On the basis of these findings, a white laser source with a color temperature of 6500 K can be synthesized. We first roughly adjust the pump intensity to reduce the conversion efficiency so that the red, green and blue lasers coexist at the output. Then, we fine-tune the coupling delay parameters so that the output power ratio meets 0.61:0.28:0.11. These research results can provide a theoretical basis for achieving efficient frequency conversion and the development of new optical devices.

Increasing social welfare with delays: strategic customers in the M/G/1 orbit queue

It is well known that strategic customers typically patronize service systems at a higher rate than the socially optimal one. Much literature has focused on inducing customers to patronize such systems at this latter rate. All of this literature considered non-idling policies that are the focus of queueing theory. We demonstrate that strategically imposing delays into such systems can improve the social welfare using the M/G/1 queue with orbit. This queue is a versatile model, that has been extensively studied in the literature from a performance evaluation perspective. In this system, customers who arrive and find the server idle begin immediately their service. However, strategic customers who find the server busy can decide whether to balk or join a virtual queue that is referred to as the orbit. Then, each time the server finishes a service, he begins to retrieve a customer from the orbit and the corresponding retrieving time is not negligible. These retrieving times can be seen as extra delays that are imposed on customers that find a busy server. We further show that when customers are strategic there are certain ranges of the parameters where strategically delaying the orbit customers can increase the welfare of a system or even maximize it. To this end, we characterize and compute the equilibrium strategies for the customers' joining/balking dilemma. We consider both the unobservable and observable versions of the system, compare them and provide some insight on the optimal delay and level of information in such systems.

Non-Linear Chaotic Features-Based Human Activity Recognition

Human activity recognition (HAR) has vital applications in human–computer interaction, somatosensory games, and motion monitoring, etc. On the basis of the human motion accelerate sensor data, through a nonlinear analysis of the human motion time series, a novel method for HAR that is based on non-linear chaotic features is proposed in this paper. First, the C-C method and G-P algorithm are used to, respectively, compute the optimal delay time and embedding dimension. Additionally, a Reconstructed Phase Space (RPS) is formed while using time-delay embedding for the human accelerometer motion sensor data. Subsequently, a two-dimensional chaotic feature matrix is constructed, where the chaotic feature is composed of the correlation dimension and largest Lyapunov exponent (LLE) of attractor trajectory in the RPS. Next, the classification algorithms are used in order to classify and recognize the two different activity classes, i.e., basic and transitional activities. The experimental results show that the chaotic feature has a higher accuracy than traditional time and frequency domain features.

Switching Time Delay Optimization for “SiC+Si” Hybrid Device in a Phase-Leg Configuration

Compared to SiC MOSFET, the switching loss of Si IGBT is much higher due to its slow switching speed and tail current. Si IGBT/SiC MOSFET hybrid switch device can reach to optimal performance with low static and dynamic loss, which can improve the current capacity of SiC devices and reduce the power loss of Si IGBT based converters. With the separated gate control signals, the switching moments of the two devices can be controlled independently to ensure Si IGBT under zero-voltage switching (ZVS) conditions. This measurement tends to reduce the switching loss of Si IGBT. However, the switching time delay between these two devices has significant impacts on its power loss. In this paper, the switching time delay optimization method is proposed to minimize the power loss of the hybrid switch. The static and dynamic characteristics of Si IGBT/SiC MOSFET hybrid-paralleled switch are studied, and a generalized power loss model for hybrid switch is developed. The influence of switching time delay on the characteristics of hybrid switch is analyzed and verified through double pulse tests in a phase-leg configuration. The experimental results show that the optimal turn-on delay time is that the two devices turn on at the same time and the turn-on loss can be reduced by about 73% compared with the solely Si IGBT and by about 52% compared with the solely SiC MOSFET. While the optimal turn-off sequence is that the Si IGBT turns off ahead of the SiC MOSFET. Under the proposed optimal turn-off delay time of the hybrid switch, the turn-off loss is reduced by about 61.4%. This optimization strategy is used in a Buck converter to verify the superiority of the SiC/Si hybrid switch and the optimal switching sequence. Simulation results show that the optimal switching sequence is consistent with theoretical analysis, and the efficiency is improved by 2.5% compared with Buck converter using solely Si IGBT.

Reconstructed State Space Features for Classification of ECG Signals.

Background: Cardiac arrhythmias are considered as one of the most serious health conditions; therefore, accurate and quick diagnosis of these conditions is highly paramount for the electrocardiogram (ECG) signals. Moreover, are rather difficult for the cardiologists to diagnose with unaided eyes due to a close similarity of these signals in the time domain.Objective: In this paper, an image-based and machine learning method were presented in order to investigate the differences between the three cardiac arrhythmias of VF, VT, SVT and the normal signal.Material and Methods: In this simulation study, the ECG data used are collected from 3 databases, including Boston Beth University Arrhythmias Center, Creighton University, and MIT-BIH. The proposed algorithm was implemented using MATLAB R2015a software and its simulation. At first, the signal is transmitted to the state space using an optimal time delay. Then, the optimal delay values are obtained using the particle swarm optimization algorithm and normalized mutual information criterion. Furthermore, the result is considered as a binary image. Then, 19 features are extracted from the image and the results are presented in the multilayer perceptron neural network for the purpose of training and testing.Results: In order to classify N-VF, VT-SVT, N-SVT, VF-VT, VT-N-VF, N-SVT-VF, VT-VF-SVT and VT-VF-SVT-N in the conducted experiments, the accuracy rates were determined at 99.5%, 100%, 94.98%, 100%,100%, 100%, 99.5%, 96.5% and 95%, respectively.Conclusion: In this paper, a new approach was developed to classify the abnormal signals obtained from an ECG such as VT, VF, and SVT compared to a normal signal. Compared to Other related studies, our proposed system significantly performed better

UAS Batch Path Planning With a Space-Time Graph

Unmanned Aircraft Systems (UAS) provide the platform of many applications such as efficient package delivery, monitoring, surveillance, search and rescue, and more. As the density of UAS deployed in urban areas for delivery and monitoring operations is expected to increase in the near future, it becomes critical to design an efficient collision-free UAS path planning system to be used by a centralized traffic manager. In this article we propose an on-demand, scalable, collision-free trajectory planning mechanism that processes routing requests in batches, with the objective of improving the ratio of successfully admitted requests. The planner transforms the input map to a unit graph discretized on the safety distance and computes trajectories using search in the derived space-time graph. The planner generates trajectories that are by design conflict-free and deadlock-free. The performance of our algorithm is analyzed with simulations. We measure admission ratio, the delay overhead vs. optimal path delay, the algorithm running time, and we compare results with prior work. The proposed batch planner yields better admission ratio and delay overhead in low and medium density scenarios. In all scenarios it has a running time that is 4-7 times shorter, showing its scalability in practical situations.

Improving the Frequency Fluctuations Attenuation of Microgrid by Determining Optimal communication System Delay and Virtual Inertia Values

Improving the Frequency Fluctuations Attenuation of Microgrid by Determining Optimal communication System Delay and Virtual Inertia Values

Correlation Analysis of Traction Load Sequences Based on Optimal Delay Method

Correlation Analysis of Traction Load Sequences Based on Optimal Delay Method

Control parameter optimization of a nonlinear vehicle suspension system with time-delayed acceleration feedback

A time-delayed acceleration feedback control is proposed to improve the vibration performance of a nonlinear vehicle suspension system. First, the harmonic balance method is applied to obtain the vertical acceleration amplitude of the system excited by simple harmonic road excitation. Then, taking the amplitude of the sprung mass acceleration and control force into account, the single-objective and multiple-objective optimization problems of time-delayed feedback control parameters, respectively, are discussed. Finally, the mathematical simulation is provided to verify the correctness of the optimization results. It is concluded that the nonlinear suspension with optimal time-delayed feedback control has better vibration control performance compared to passive one. The acceleration amplitude of the sprung mass is significantly reduced by the single-objective optimization of the control parameters. Moreover, when the optimal time delay is introduced, the active control force input is fewer than that without time delay. The phenomenon of energy transfer between the sprung mass and the unsprung mass is observed in some road-excitation frequencies.

Optimal delayed control of primary and second resonances of an electrostatic driving double-sided micro-actuator

Abstract In this paper, an electrostatic driving double-sided micro-actuator was studied based on the fully clamped micro-beam with a uniform thickness. An analysis of primary, superharmonic and subharmonic resonances with two distinct time delays was investigated. The multiple scales perturbation method was used to solve the nonlinear equation without large deformation. Steady-state solutions and their stabilities under each resonance conditions were studied. The optimal time delay was obtained for controller design. The effect of the feedback gains and time delays on the nonlinear response of the system was discussed and the analysis shows that a suitable choice of the feedback gains and time delayed quantity can reduce the nonlinearity, resonance region and unstable multi-solutions, also improve the efficiency of the vibration control. It is believed that the results of this paper will be valuable in the design of optimal controllers.

Generalised bisection method for optimum ultrasonic ray tracing and focusing in multi-layered structures

Ultrasonic testing has been used for many decades, proving itself very efficient for detecting defects in many industrial sectors. The desire to apply ultrasonic testing to geometrically complex structures, and to anisotropic, inhomogeneous materials, together with the advent of more powerful electronics and software, is constantly pushing the applicability of ultrasonic waves to their limits. General ray tracing models, suitable for calculating the proper incident angle of single element probes and the proper time delay of phased array, are currently required. They can support the development of new imaging techniques, as Full Matrix Capture and Total Focusing Method, and the execution of very challenging ultrasonic inspections. This paper introduces a generalized iterative method for the computation of ultrasonic ray paths, when ultrasonic source and target are separated by multiple complex material interfaces in the two dimensional and three dimensional domains. The manuscript starts with a review of the well-known bisection method, and extends the applicability of the method to cases with increasing complexity. An application example, in the field of in-process weld inspection, shows that the introduced generalised bisection method can enable the computation of optimum incidence angles and focal delays for accurate ultrasonic focusing. There is no restriction on the analytical interfaces to be surjective. Interface folding is permitted. It is not necessary to know, a priori, with what sequence the interfaces are crossed by the rays. The presented implementation of the method completes each iteration of the bisection method in 4 ms, for a case with a single interface, and in 960 ms for the case with 52 interfaces.

Lag Variables in Nitrogen Oxide Concentration Modelling: A Case Study in Wrocław, Poland

Due to the unwavering interest of both residents and authorities in the air quality of urban agglomerations, we pose the following question in this paper: What impact do current and past meteorological factors and traffic flow intensity have on air quality? What is the impact of lagged variables on the fit of an explanation model, and how do they affect its ability to predict? We focused on NO2 and NOx concentrations, and conducted this research using hourly data from the city of Wrocław (western Poland) from 2015 to 2017; we used multi-objective optimization to determine the optimal delays. It turned out that for both NO2 and NOx, the past values for traffic flow, wind speed, and sunshine duration are more important than the current ones. We built random forest models on each of the pollutants for both the current and past values and discovered that including a lagged variable increases the resulting R2 from 0.51 to 0.56 for NO2 and from 0.46 to 0.52 for NOx. We also analyzed the feature importance in each model, and found that for NO2, a wind speed delay of more than three hours causes a significant decrease, while the importance of relative humidity increases with a seven-hour delay; likewise, wind speed increases the importance for NOx prediction with a two-hour delay. We concluded that, in pollutant concentration modeling, the possibility of a delayed effect of the independent variables should always be considered, because it can significantly increase the performance of the model and suggest unexpected relationships or dependencies.

Insights into Enhanced Repeatability of Femtosecond Laser-Induced Plasmas.

Repeatability is of utmost importance as it is directly linked to measurement accuracy and precision of a technique and affects its cost, utility, and commercialization. The present paper contributes to explain enhanced repeatability of the femtosecond laser-induced breakdown spectroscopy (fs-LIBS) technique, remarkably significant for its industrial applications and instrumental size reduction. A fs-laser with 7 mJ pulse energy was focused to create a transient titanium plasma, and a high-resolution spectrometer was used to study time-resolved spectra and single-shot drilling sampling repeatability. Time-resolved spectroscopy study at a delay time interval of 0–1600 ns showed 200–400 ns as the optimum delay time zone for data acquisition with 2–4% line intensity RSDs. Plasma temperature RSDs were <1.8% for the investigated delay interval and reached 0.5% at 200 ns where the temperature recorded a maximum value of 22,000 K. Electron density reached 5.7 × 1017 cm–3 at 200 ns, and RSDs were <3% with the least fluctuation of 0.7%. Shot-to-shot RSDs were 3.5–5% at 15–30 drilling shot intervals for line intensities, <2% for plasma temperature, and <6.5% for electron density. Using an uncertainty propagation formula, total number density RSDs were calculated to be 1.9–5.3% for 50 single-shot drilling scenarios. Considering physics behind results, fs-plasmas are “stable ablation sources” due to their electrostatic formation mechanisms and confined hydrodynamic evolution. The fs-laser opens up new directions for LIBS applications where accuracy is significantly enhanced.

Effect of plasma hydrodynamics on laser-produced bremsstrahlung MeV photon dose

We detail a laser plasma experiment aimed at enhancing laser to MeV electron energy coupling and then the x-ray dose produced when a short pulse laser propagates through a long preformed plasma. This study can be of interest not only for radiography of high areal mass objects requiring large doses but also for radiation safety of large scale laser facilities such as LMJ or NIF able to produce long preformed plasmas through which a short pulse laser can propagate. A low-intensity (∼1014 W/cm2) ns beam explodes a thin foil deposited on a high-Z solid target to generate an underdense plasma. An intense (&amp;gt;1018 W/cm2) and short (&amp;lt;1 ps) laser pulse then (with an adjustable delay δt) interacts with this plasma and produces multi-MeV electrons. These high-energy electrons are converted into a bremsstrahlung emission of MeV x-ray photons in the high-Z target. In a second target design, a vacuum gap between the foil and the conversion target is also tested to let the plasma expand on both sides of the foil, increasing the interaction length even more. Results show how the vaporization of the foil produces an underdense plasma over several hundreds of micrometers which significantly enhances x-ray doses, with harder x-ray spectra obtained at an optimum delay, δt, until the short pulse laser is affected by refraction. Increasing the interaction length with gap targets is at the origin of a much more complex plasma hydrodynamics involving on-axis plasma stagnation which delays the optimum time for the maximum x-ray dose production.

Integer Linear Programming Based Topology Design for GNSSs With Inter-Satellite Links

Inter-satellite links (ISLs) can be employed in global navigation satellite systems (GNSSs) for space-based telemetry, telecommand and ranging, which reduces the requirement for a large number of ground stations (GSs). However, the polling time division duplex (PTDD) ranging hierarchy of the ISLs raises the topology design problem of the networks. To optimize the communication performance with the constraint of ranging for precise orbit determination in GNSSs, we model the ISLs network with finite state automation (FSA) and solve the optimization problem with integer linear programming (ILP). With the proposed method, for the first time, optimal delay and throughput are both achieved for data transmission between satellites and GSs with guaranteed ranging performance. Simulation results corroborate that, compared with two existing methods, the proposed scheme largely improves the communication performance, i.e., the average delay and the network throughput by 46.9% and 11%, respectively.

Lifetime Responsive Depth Based Routing for Underwater Wireless Sensor Network using Hybrid Soft Computing Technique with Optimal Delay

Underwater wireless sensor network (UWSN) is an emerging technology that has been used for different applications such as warning systems for disasters, monitoring the ecosystem, drilling of the oil, defense surveillance. Although underwater communication may be accomplished using electromagnetic or optical waves, but these methods are not feasible for practical UWSN, due to signal attenuation. UWSN faces several issues like restricted bandwidth, irregular node mobility, increased delay etc. which affects the routing behavior. In this paper, an optimal delay and lifetime aware depth based routing (ODLDR) protocol is proposed. Protocol first introduced the group partitioning algorithm for cluster formation that minimizes the energy consumption of network then an efficient priority based scheduling algorithm is proposed for trust computation, which helps in finalizing the CH and routing path. The ODLDR protocol is tested with the high density nodes in Network Simulator (NS2) tool. The simulation results shows the effectiveness of the ODLDR protocol in terms of energy consumption, packet delivery ratio, positioning accuracy, end-to-end delay, throughput and network lifetime.

A Variable-Frequency Current-Dependent Switching Strategy to Improve Tradeoff Between Efficiency and SiC MOSFET Overcurrent Stress in Si/SiC-Hybrid-Switch-Based Inverters

Reliability remains an issue for the Si/SiC hybrid switch adopting the conventional switching strategy of the internal SiC MOSFET that turns on earlier, and off later. Such issue is attributable to the overcurrent stress under the heavy load operating condition, which adversely affects the SiC MOSFET during the gate delay time. To solve this problem without increasing the extra power loss, a novel variable-frequency current-dependent switching strategy combining the variable switching pattern strategy, and the variable pulsewidth modulation (PWM) frequency strategy is proposed. Variable switching pattern strategy can avoid the overcurrent stress of the SiC MOSFET at the heavy load operating condition, and the designed optimal delay time in different switching patterns can achieve the compromise between the excellent reliability, and the power loss of Si/SiC hybrid switch. Variable PWM frequency strategy can effectively reduce the switching loss of the Si/SiC hybrid switch by decreasing the switching frequency around the peak current region. An Si/SiC-hybrid-switch-based single-phase inverter platform is constructed and tested. Test results show that the power loss of the single-phase inverter adopting such switching strategy outperforms the current-dependent switching strategy with 9.4% reduction of power loss, and overcurrent stress of SiC MOSFET is avoided.

Optimum MDC FFT Hardware Architectures in Terms of Delays and Multiplexers

In this brief, we show how to derive all the optimum multi-path delay commutator (MDC) fast Fourier transform (FFT) hardware architectures in terms of delays and multiplexers and calculate the number of such architectures. The proposed approach is based on analyzing the orders at the FFT stages that lead to optimum number of delays and multiplexers. The results show that there exist a large number of optimum MDC FFTs. This large design space can be explored in the future in order to design efficient MDC architectures that not only optimize the number of delays and multiplexers, but also other figures of merit such as the number of rotators or the input/output data order.