Finite Period Of Time Research Articles

Distributed Finite-Time Consensus Tracking Control for Nonlinear Multi-Agent Systems With FDI Attacks and Application to Single-Link Robots

This brief considers the distributed finite-time consensus tracking control problem for nonlinear multi-agent systems with false data injection (FDI) attacks. Firstly, since instability is inevitable when false datas are injected into the researched system, a security control algorithm combining the modified coordinate transformation and the dynamic surface control (DSC) method is developed to eliminate the negative impact of FDI attacks and reduce the burden caused by iterative computations of virtual controls. Besides, there are unknown nonlinearities in the dynamics of each agent, which can not be directly handled by the traditional control design. Thus, the neural-network-based approximation technique is introduced to compensate the unknown nonlinearities. In summary, a novel controller is constructed for each agent, which guarantees the consensus of the outputs of all agents can be achieved and that all the signals of the studied system are bounded within a finite-time period. To prove the correctness of the designed security control algorithm, a simulation example of the multi-agent system composed of multiple single-link robots is presented.

Shear Flow Instability over a Finite Time Interval

Within the framework of a discrete quasi-geostrophic model with two vertical levels, the problem of linear stability of the flow of a stratified rotating fluid with constant vertical and horizontal velocity shifts is solved. It is shown that taking into account the horizontal shear leads to a qualitative change in the dynamics of unstable wave disturbances. The main feature is related to the effect of temporary exponential growth of unstable perturbations, i.e. growth over a finite time period. This effect manifests itself in the alternation of stages of smooth oscillating behavior (in time) with stages of exponential (explosive) growth of finite duration. A kinematic interpretation of the effect of temporal exponential growth is given, which is associated with the passage of a time-dependent perturbation wave vector through the region of exponential instability that exists in the absence of a horizontal shear. It is shown that mathematically this effect is described by solutions of a second-order differential equation containing turning points. Asymptotic solutions of the equation are given for weak horizontal shifts.

An Adaptive Backstepping Sliding-Mode Control for Improving Position Tracking of a Permanent-Magnet Synchronous Motor With a Nonlinear Disturbance Observer

To provide reliable position control for a permanent-magnet synchronous motor (PMSM) under conditions of lumped disturbances such as external load torque fluctuation and system parameter variation, an adaptive backstepping sliding-mode control (ABSMC) with a nonlinear disturbance observer (NDO) is proposed. An ABSMC is a non-cascade technique that employs a position-current single-loop control structure rather than a conventional cascade control structure for vector control of the PMSM. This method uses Lyapunov theory to design a control law to ensure the motor position reaches a desired value in a finite period of time and consequently achieves a rapid transient response. The proposed ABSMC incorporates an adaptive convergence gain to avoid a large overshoot under point-to-point position command. The NDO with a nonlinear observer gain is proposed to estimate unknown disturbances and provide feed-forward compensation for the ABSMC, improving robustness and reducing steady-state position error. The proposed methods are applied to an industrial motor drive to confirm their validity in real-world operating environments.

A METHODOLOGY OF OPERATIVE DIAGNOSTICS OF THE RHYTHMIC WORK OF MINING ENTERPRISES ACCORDING TO THE DYNAMICS OF ELECTRICITY CONSUMPTION

Purpose. The aim of the article is the development of a methodology for separate operational diagnostics of the rhythmicity of the work of several quarries working as part of a mining and transport complex, which makes it possible to assess the contribution of each quarry to the formation of the production cost of a mining enterprise. Methodology of research. The research methodology includes the analysis of known methods and formulas for estimating the rhythmicity of a mining enterprise by the volume of products produced in a finite period of time, the transition in known formulas from the volume of products through the specific consumption of electricity to the consumption of electrical energy and electrical power per unit of time. The methods of spectral analysis, electrical engineering and energy management were used in the development of the method of assessing the rhythmicity of the mining and transport complex. Findings. The diagnosis of the rhythmicity of the work of each of the quarries operating in one mining and transport complex of the mining enterprise was carried out according to the dispersion of fluctuations of the electrical active power consumed by the crushing plant in the range of operating frequencies characteristic of each quarry. The dependence of the resonance frequencies of the spectral density of the fluctuations of the electrical power parameters of the crushing plant on the periods and volumes of ore supply from each pit of the mining enterprise was established. A methodology of separate operational assessment of the rhythmicity of the work of several quarries of a mining enterprise based on the dynamics of energy consumption of a crushing plant was developed, which allows to assess the rhythmicity of the work of each quarry and the mining and transport complex of the mining enterprise as a whole and to manage it. Originality. For the first time, the dependence of the resonance frequencies of the spectral density of fluctuations in the power consumption dynamics of the crushing plant on the periods of ore supply from each pit of the mining enterprise was established. Practical value. The developed methodology allows quickly to manage the logistics parameters of the supply of ore from the quarries of the mining enterprise, to increase the rhythm of production and to reduce the cost of production. Key words: rhythmicity of production, quarries, mining enterprises, cost of production, diagnostics.

Epidemics from the Eye of the Pathogen

While a common trend in disease modeling is to develop models of increasing complexity, it was recently pointed out that outbreaks appear remarkably simple when viewed in the incidence vs. cumulative cases (ICC) plane. This article details the theory behind this phenomenon by analyzing the stochastic SIR (Susceptible, Infected, Recovered) model in the cumulative cases domain. We prove that the Markov chain associated with this model reduces, in the ICC plane, to a pure birth chain for the cumulative number of cases, whose limit leads to an independent increments Gaussian process that fluctuates about a deterministic ICC curve. We calculate the associated variance and quantify the additional variability due to estimating incidence over a finite period of time. We also illustrate the universality brought forth by the ICC concept on real-world data for Influenza A and for the COVID-19 outbreak in Arizona.

Smooth, Singularity-Free, Finite-Time Tracking Control for Euler–Lagrange Systems

This paper investigates the problem of constrained finite-time tracking control of Euler–Lagrange systems subject to system uncertainties and external disturbances. Firstly, we introduce a nonsingular, fast, constrained terminal sliding manifold (NFCTSM) that contains a time-varying gain to deal with the output tracking error constraint. Therefore, the desired performance in steady-state and transience such as ultimate-tracking-error bound, maximum overshoot, and convergence speed are provided. Then, based on the proposed NFCTSM, a smooth adaptive finite-time control is designed such that the tracking errors converge to an arbitrary small region around the origin during a finite period of time. Moreover, the square of the upper bound of the lumped uncertainty is estimated by the adaptive law in order not to use the discontinuous signum function. The efficacy and usefulness of the proposed control methodology are demonstrated via simulation results and comparison with relevant works.

A review of reproducible and transparent research practices in urology publications from 2014 to2018

BackgroundReproducibility is essential for the integrity of scientific research. Reproducibility is measured by the ability of different investigators to replicate the outcomes of an original publication using the same materials and procedures. Unfortunately, reproducibility is not currently a standard being met by most scientific research.MethodsFor this review, we sampled 300 publications in the field of urology to assess for 14 indicators of reproducibility including material availability, raw data availability, analysis script availability, pre-registration information, links to protocols, and if the publication was available free to the public. Publications were also assessed for statements about conflicts of interest and funding sources.ResultsOf the 300 sample publications, 171 contained empirical data available for analysis of reproducibility. Of the 171 articles with empirical data to analyze, 0.58% provided links to protocols, 4.09% provided access to raw data, 3.09% provided access to materials, and 4.68% were pre-registered. None of the studies provided analysis scripts. Our review is cross-sectional in nature, including only PubMed indexed journals-published in English-and within a finite time period. Thus, our results should be interpreted in light of these considerations.ConclusionCurrent urology research does not consistently provide the components needed to reproduce original studies. Collaborative efforts from investigators and journal editors are needed to improve research quality while minimizing waste and patient risk.

A Macro-Theoretic Exploration of Some Covid-19 Induced Constraints on Economic Policy

ABSTRACT The Covid-19 pandemic has spawned a crisis whose dimensions encompass the domains of health and the economy. The latter is on account of the use of non-pharmaceutical interventions such as lockdowns in order to deal with a highly contagious disease. Though some vaccines have emerged, lockdowns of varying degrees are still required since geographical coverage of vaccines is uneven, the protection afforded by vaccines is only for a finite period of time and new variants may escape existing vaccines. This provides the context within which economic policy could intervene. Monetary policy is either unavailable or ineffective, especially when the neoliberal project is hegemonic. Therefore, the specific policy instrument that tends to be utilised is fiscal policy wherein it is postulated that the government tries to achieve a target degree of capacity utilisation. It is demonstrated within the framework of a heterodox macroeconomic model that considerations involving macroeconomic stability (and political economy more generally) may cause this target to be below what is warranted by public health requirements. The paper concludes with some suggestions for future work in this research direction.

Distributed Finite-Time Event-Triggered Frequency and Voltage Control of AC Microgrids

This paper proposes a finite-time event-triggered secondary frequency and voltage control for islanded AC microgrids (MGs) in a distributed fashion. The proposed control strategy can effectively perform frequency restoration and voltage regulations, while sharing the active and reactive power among the distributed generators (DGs) based on their power ratings. The finite-time control enables a system to reach consensus in a finite period of time enhanced from the asymptotic convergence. The event-triggered communication is utilized to reduce the communication burden among the DG controllers by transmitting data among DGs if an event-triggering condition is satisfied. The performance of the proposed finite-time event-triggered frequency control is verified utilizing a hardware-in-the-loop experimental testbed which simulates an AC MG in Opal-RT.

Modeling Immigration in Spain: Causes, Size and Consequences

This paper deals with the construction of a discrete dynamic population model addressed to estimate the expected size of the immigration population in a finite short period of time in Spain. By paying attention to a special subpopulation of interest, such as an irregular immigrant, unaccompanied minor immigrant and regular immigrant, a vector discrete population model is built after the discussion and introduction of proper hypotheses linked to economy, host and country of origin regulation policies, political interest and others. The model allows us to study the change of the results under variation of the parameters.

GAME CONTROL OF A FILTER WITH A RANDOM JUMP STRUCTURE

The game problem of synthesis of information-control algorithms of filtering of two opposing sides is considered. The opponents’ control objects are described by multidimensional linear stochastic recurrent equations. Each side controls the covariance of the output signals of its object and the covariance of additive signals in the channels of the enemy object meters. Covariances of noise signals of an object characterize the power of disturbances, and covariances of noise signals of meters characterize the power of interference.The goal of each player’s management is to reduce the filtering error of their system and at the same time increase the filtering error of the opponent’s system. The criterion of optimal control of one player is the minimax, and the other is the maximin of the average value of the quality indicator for a finite period of time. Quality indicators consist of a linear combination of three particular indicators, the first of which is the probability of one of the two states of the Markov jump structure, and the other two are restrictions on the probabilities of transitions of the Markov chain. Observation systems consist of structure indicators and meters of one-time coordinates. Each information-control algorithm is a set of five interconnected blocks: a structure classifier, a structure indicator, a regulator, a dispersiometer and a filter. The obtained information-control algorithms are described by a closed system of recurrent equations. The algorithms are based on the methods of the theory of multistep antagonistic games, the theory of systems with a random jump structure, stochastic dynamic programming and Bayesian filtering. An example of the construction of game information-control algorithms of two unmanned aerial vehicles of the opposing sides, aimed at the objects of the opponents, is considered.

Observer-based adaptive fuzzy finite-time tracking control of switched nonlinear systems

In this article, we investigate the finite-time output feedback control issue for switched nonlinear systems. In the design procedure, fuzzy logic systems are used for identifying the unknown functions in switched nonlinear systems. A common state observer is constructed such that the unmeasured states can be measured. Based on the framework of the backstepping algorithm, an observer-based finite-time adaptive tracking control strategy is proposed via the common Lyapunov function approach. The stability analysis process confirms in detail that all the closed-loop signals are bounded under arbitrary switchings and the tracking error can converge to a small neighbourhood of the origin after a finite period of time. In order to verify the feasibility of the proposed control scheme, a numerical simulation example is shown in this paper.

Varibox encryption algorithm : The new generation of hybrid security measure for the era of quantum computation

The continual proliferation and evolution of the Internet of Things (IoT) domain is posing serious security threats to the whole network. In IoT, the insecure communication channel between sensors and the Internet can lead to malicious penetrations. Poor computational resources in traditional sensors critically constraint and impact the execution of conventional security algorithms among IoT devices. Consequently, lightweight security algorithms turn out to be a feasible alternative. To keep up with the existent Internet security level, this work proposes a new security scheme that employs a unique methodology based on a one-way counter value hashing table i.e. VariBox. This scheme integrates modular arithmetic applied on Unicode UTF-16 encoding standards coupled with AES and RSA algorithms. The proposed methodology effectively offers i) low computational overhead i.e. overall processing time of 0.1 seconds (VariBox processing time 0.003 seconds) and ii) enhances the overall security of the IoT data transfer model. Once this model is employed, the overall spectrum of potential brute force solutions will be rendered computationally expensive and infeasible to be calculated within a finite time period.

Robust one-way trading with limited number of transactions and heuristics for fixed transaction costs

A one-way trader has a certain amount of goods to trade over a finite period of time, but faces price uncertainties for which a probability distribution is unavailable. The problem becomes even more complicated with fixed transaction cost, which is very common in real world. Limiting the total number of transactions to control for transaction costs seems straightforward, but how to implement this effectively in real time with efficient algorithms backed by theoretical results is a big challenge and has not been well studied in the literature. Such one-way trading problem with limited number of transactions is formulated in a robust optimization framework. Theoretical analysis finds the optimal trading strategy with closed-form solution, identifies the worst price scenarios to help gain trading insights and spot trading opportunities, and shows that in the worst scenario, all of the optimal trades are of equal amount. On the practice side, a highly efficient heuristic to deal with fixed transaction costs is designed by choosing a proper limit on the number of transactions and merging trades on the fly, whose effectiveness and robustness are demonstrated by numerical experiments. The heuristic for selling employs a dynamic scheme with gradually increasing reservation price, in stark contrast to the static scheme with decreasing reservation price when the price distribution is known, which helps explain the robust performance of the proposed heuristic.

APPLICATION OF RENEWAL REWARD PROCESSES IN HOMOGENEOUS DISCRETE MARKOV CHAIN

A renewal process which is a special type of a counting process, which counts the number of events that occur up to (and including) time has been investigated, in order to provide some insight into the performance measures in renewal process and sequence such as, the mean time between successive renewals, ; Laplace-Stiltjes transform (LST) of the mean time, ; the Laplace-Stieltjes transform (LST) of the mean time distribution function, ; Laplace-Stiltjes transform (LST) of fold convolution of distribution function, ; the time at which the renewal occurs, the average number of renewals per unit time over the interval (0, t], and expected reward, . Our quest is to analyse the distribution function of the renewal process and sequence using the concept of discrete time Markov chain to obtain the aforementioned performance measures. Some properties of the Erlang , exponential and geometric distributions are used with the help of some existing laws, theorems and formulas of Markov chain. We concluded our study through illustrative examples that, it is not possible for an infinite number of renewals to occur in a finite period of time; Also, the expected number of renewals increases linearly with time; and from the uniqueness property, we affirmed that, the Poisson process is the only renewal process with a linear mean-value function; and lastly, we obtained the optimal replacement policy for a manufacturing machine which showed that, the exponential property of the lifetime

Trajectory tracking for non-Markovian quantum systems

We propose a systematic scheme to engineer quantum states of a quantum system governed by a time-convolutionless non-Markovian master equation. According to the idea of reverse engineering, the general algebraic equation to determine the control parameters, such as coherent and incoherent control fields, is presented. Without artificially engineering the time-dependent decay rates and retaining the environment-induced Lamb shifts, the quantum state can still be transferred into the target state in a finite period of time along an arbitrary designed trajectory strictly in Hilbert space. As an application, we apply our scheme to a driven two-level non-Markovian system and realize instantaneous-steady-state tracking and a complete population inversion with control parameters which are available in experimental settings.

A time-stepping method for multibody systems involving frictional impacts and phases with persistent contact

This work complements and continues efforts towards developing a complete numerical integration method for multibody dynamic systems with frictional impacts. Specifically, the new method is a time-stepping scheme, which is applicable to mechanical systems subject to a set of bilateral and a single unilateral motion constraint. During an impact free phase of the motion, a suitable augmented Lagrangian methodology is applied. When an impact is detected during a time step, the post-impact state is determined by employing a special process, which addresses properly the inherent numerical stiffness associated with the impact events. The basic contribution of the present study is the extension to cover cases where the contact between the interacting bodies is possible to exist for a finite period of time after an impact. This phenomenon occurs frequently in machines and mechanisms and is known as persistent contact. First, a complete strategy is developed for establishing a general numerical procedure for capturing and treating both activation of contact and loss of contact between two bodies. Then, the accuracy and efficiency of this procedure is tested and demonstrated by applying it to a selected set of mechanical examples.

Saturated super-twisting sliding mode missile guidance

This paper concentrates on developing a missile terminal guidance law against a highly maneuvering target whose maneuvering acceleration is very close to that of the missile or even exceeds the missile normal acceleration in a finite period of time. A new saturated super-twisting algorithm is proposed and applied to the design of missile guidance law. The proposed algorithm has the advantages of simple structure, easy parameter tuning rules and a full utilization of the limit control input. The designed saturated super-twisting sliding mode guidance law is then employed in a missile guidance system. Simulation and its superior performance against strong maneuvering targets is demonstrated.

Magnetized Dusty Black Holes and Wormholes

We consider the generalized Tolman solution of general relativity, describing the evolution of a spherical dust cloud in the presence of an external electric or magnetic field. The solution contains three arbitrary functions f(R), F(R) and τ0(R), where R is a radial coordinate in the comoving reference frame. The solution splits into three branches corresponding to hyperbolic (f>0), parabolic (f=0) and elliptic (f<0) types of motion. In such models, we study the possible existence of wormhole throats defined as spheres of minimum radius at a fixed time instant, and prove the existence of throats in the elliptic branch under certain conditions imposed on the arbitrary functions. It is further shown that the normal to a throat is a timelike vector (except for the instant of maximum expansion, when this vector is null), hence a throat is in general located in a T-region of space-time. Thus, if such a dust cloud is placed between two empty (Reissner–Nordström or Schwarzschild) space-time regions, the whole configuration is a black hole rather than a wormhole. However, dust clouds with throats can be inscribed into closed isotropic cosmological models filled with dust to form wormholes which exist for a finite period of time and experience expansion and contraction together with the corresponding cosmology. Explicit examples and numerical estimates are presented. The possible traversability of wormhole-like evolving dust layers is established by a numerical study of radial null geodesics.

Dirac Spatial Search with Electric Fields.

Electric Dirac quantum walks, which are a discretisation of the Dirac equation for a spinor coupled to an electric field, are revisited in order to perform spatial searches. The Coulomb electric field of a point charge is used as a non local oracle to perform a spatial search on a 2D grid of N points. As other quantum walks proposed for spatial search, these walks localise partially on the charge after a finite period of time. However, contrary to other walks, this localisation time scales as for small values of N and tends asymptotically to a constant for larger Ns, thus offering a speed-up over conventional methods.