Discrete Dynamic Model Research Articles

From Discrete to Continuous Modeling of Lymphocyte Development and Plasticity in Chronic Diseases.

The molecular events leading to differentiation, development, and plasticity of lymphoid cells have been subject of intense research due to their key roles in multiple pathologies, such as lymphoproliferative disorders, tumor growth maintenance and chronic diseases. The emergent roles of lymphoid cells and the use of high-throughput technologies have led to an extensive accumulation of experimental data allowing the reconstruction of gene regulatory networks (GRN) by integrating biochemical signals provided by the microenvironment with transcriptional modules of lineage-specific genes. Computational modeling of GRN has been useful for the identification of molecular switches involved in lymphoid specification, prediction of microenvironment-dependent cell plasticity, and analyses of signaling events occurring downstream the activation of antigen recognition receptors. Among most common modeling strategies to analyze the dynamical behavior of GRN, discrete dynamic models are widely used for their capacity to capture molecular interactions when a limited knowledge of kinetic parameters is present. However, they are less powerful when modeling complex systems sensitive to biochemical gradients. To compensate it, discrete models may be transformed into regulatory networks that includes state variables and parameters varying within a continuous range. This approach is based on a system of differential equations dynamics with regulatory interactions described by fuzzy logic propositions. Here, we discuss the applicability of this method on modeling of development and plasticity processes of adaptive lymphocytes, and its potential implications in the study of pathological landscapes associated to chronic diseases.

Dynamics analysis for a discrete dynamic competition model

In this paper, the dynamics of a discrete market share attraction model are investigated. It shows that the system can undergo flip bifurcation and chaos. The stability and bifurcation of a market share attraction model are analyzed by using the bifurcation theory and the center manifold theorem. The system displays complex dynamical behaviors, including period-1, 2, 4, 6, 8, 16 orbits, invariant cycle, a cascade of period-doubling, quasi-periodic orbits, and the chaotic sets. Numerical simulations illustrate the analysis and results.

Effects of Holocene climate changes on alpine ecosystems: Nonequilibrium dynamics drive insect species richness on alpine islands

AbstractAimTo identify the effect of multiple, temporally close, forcing events (i.e. climate‐driven habitat fragmentations/homogenizations) in shaping current patterns of biodiversity in alpine areas. Given their spatial configuration, alpine areas have been traditionally seen as islands surrounded by an “ocean” of unsuitable lands. A quantitative assessment of the effects of Holocene climate fluctuations on islands area and inter‐island connectivity is crucial to finely reconstruct past biodiversity dynamics and forecast species responses to future changes.LocationItaly.TaxaCarabidae (Ground beetles), Chrysomelidae (Leaf beetles), Elateridae (Click beetles), Orthoptera (Grasshoppers and Crickets) and Papilionoidea (Butterflies and Skippers).MethodsA total of 1,077 species for 128,093 records were analysed and a classification based on their functional traits allowed identifying groups of good and poor dispersers within each taxon. A dynamic discrete model of ecosystem evolution provided the spatio‐temporal context to test two competing (transient equilibria vs. nonequilibrium) dynamics based on different colonization capabilities. In the transient equilibria dynamic the species are able to respond to island evolution through successful dispersal and colonization events, whereas in the nonequilibrium dynamic ineffective immigration constrains the current species richness to that generated by the strongest island contraction.ResultsWith the exception of Elateridae, good dispersers (Chrysomelidae and Papilionoidea) responded to environmental changes by establishing a series of transient equilibria. In contrast, the nonequilibrium dynamic better described patterns of species richness in poor dispersers (Carabidae and Orthoptera).Main conclusionsOur approach could be used as the basis for the development of spatially and temporally explicit models of island evolution and could be a valuable tool for quantifying the sensitivity of single taxa to climate‐driven habitat changes. It also represents a further step towards the forecasting of future responses to climate change and the accompanying development of conservation strategies that more effectively respond to the detrimental impacts of climate change on biodiversity.

Influence of Excess Volumes Induced by Re and W on Dislocation Motion and Creep in Ni-Base Single Crystal Superalloys: A 3D Discrete Dislocation Dynamics Study

A comprehensive 3D discrete dislocation dynamics model for Ni-base single crystal superalloys was used to investigate the influence of excess volumes induced by solute atoms Re and W on dislocation motion and creep under different tensile loads at 850 ° C. The solute atoms were distributed homogeneously only in γ matrix channels. Their excess volumes due to the size difference from the host Ni were calculated by density functional theory. The excess volume affected dislocation glide more strongly than dislocation climb. The relative positions of dislocations and solute atoms determined the magnitude of back stresses on the dislocation motion. Without diffusion of solute atoms, it was found that W with a larger excess volume had a stronger strengthening effect than Re. With increasing concentration of solute atoms, the creep resistance increased. However, a low external stress reduced the influence of different excess volumes and different concentrations on creep.

Oba Filter for Online-Adaptive Nonlinear State Estimation With Interference

Interference, such as jamming, is widely encountered in practical applications, such as target tracking. Kalman-based nonlinear filters may not be feasible for nonlinear state estimation with nonlinearly transformed interference. This paper presents an online-based adaptive (oba) filter, which we have named the oba filter (OF), for state filtering and prediction of nonlinear discrete dynamic models with estimate constraints, nonlinearly transformed interference and noise. In the OF, noises and interference are approximated by discrete noises and interference; states are quantized; some undesired state estimates, which are not in near vicinities of the actual state values, are detected by a confidence level, and then state quantization levels are updated at the times when undesired estimates occur by using the measurement model; and states are recursively estimated by a suboptimal implementation of multiple composite hypothesis testing. The OF can prevent some undesired state estimates and outperform the unscented Kalman, regularized, sampling importance resampling (SIR), and auxiliary SIR particle filters for some nonlinear models with noise and interference. It is also suitable for state estimation with either missing observations or estimate constraints.

Study of ball screw system preload monitoring during operation based on the motor current and screw-nut vibration

Abstract In this paper, we propose a method to monitor the preload of an operational ball screw drive system mostly used in CNC machine tools by evaluating the natural frequency of the screw nut in the axial direction and the corresponding working table displacement. First, we derived a discrete dynamic model and used it to study the variation in the ball screw system preload. Second, we proposed a method for monitoring the ball screw preload in operational mode via the motor current signal and the screw nut axial vibration signal. We apply this method by acquiring and analyzing the signals from the system as it undergoes a transition in its motion, then compose the frequency response function (FRF) of the ball screw system. This enables us to detect the axial natural frequency of the ball screw drive system. The ball screw preload is then calculated and monitored as the system is operational. We provide an efficient and intuitive method to monitor the variation in preload level of an operational ball screw system. This method can be used as an indicator of the health status of the drive system in particular, as well as for the entire machine tool in general.

СРАВНИТЕЛЬНЫЙ АНАЛИЗ РАСЧЕТНО-ДИНАМИЧЕСКИХ МОДЕЛЕЙ ПОРТОВЫХ КРАНОВ НА ОСНОВЕ ОДНО- И ДВУМЕРНЫХ КОНЕЧНЫХ ЭЛЕМЕНТОВ

The finite element method is widely used in strength calculations of machine-building structures and has a significant list of basic finite elements used to build the discrete finite element computable dynamic models of load-lifting cranes. The article describes static and dynamic characteristics of a computable dynamic model (CDM). CDM is designed to determine stiff features (developing stiffness matrix) and to define the deflected mode of the structures by using different means in structural mechanics, which have been chosen by a designer. Dynamic parameters are determined according to CDM to describe eigen and forced oscillations of crane structures under external action. The quality analysis of CDM of bearing metal structures of bridge cranes built on the basis of bar-shaped open and closed profiles and plate finite elements is based on comparison of the total flexural rigidity of the girders and eigen frequencies and eigenforms of oscillations of their CDM. The general methodology for building equations of motion for crane systems with many (n) degrees of freedom is based on their bar and plate finite elements, the latter are based on Kirchhoff theory of plates. Comparative analysis of the eigenforms of oscillations of the plate and bar CDM of crane with 130/32 t and 33.5m span has been given, the advantages of two types of CDM important for design analysis of strength and seismic resistance in designing bridge cranes are revealed. There has been substantiated the need to develop new methods of calculating finite element models taking into account the dimensional effect. The structures are recommended to regard as unified dimensional systems allowing for different types of non-linearity.

Simultaneous evacuation and entrance planning in complex building based on dynamic network flows

• This paper presents mathematical models that address the simultaneous evacuation of victims and entrance of responders. • Solutions provide the optimal routes for evacuees and responders within a critical timeframe. • Four types of models are developed according to the three different degrees of the golden time. • A heuristic algorithm is developed by extending the capacity constrained route planner. This paper presents mathematical models and a heuristic algorithm that address a simultaneous evacuation and entrance planning. For the simultaneous evacuation and entrance planning, four types of mathematical models based on the discrete time dynamic network flow model are developed to provide the optimal routes for evacuees and responders within a critical timeframe. The optimal routes obtained by the mathematical models can minimize the densification of evacuees and responders into specific areas. However, the mathematical model has a weakness in terms of long computation time for the large-size problem. To overcome the limitation, we developed a heuristic algorithm. We also analyzed the characteristics of each model and the heuristic algorithm by conducting case studies. This study pioneers area related to evacuation planning by developing and analyzing four types of mathematical models and a heuristic algorithm which take into account simultaneous evacuation and entrance planning.

Correction to: Discrete dynamical Pareto optimization model in the risk portfolio for natural disaster insurance in China

The original article, Discrete dynamical Pareto optimization model in the risk portfolio for natural disaster insurance in China, in Natural Hazards (2018) 90: 445–460, was published without the provided reference below.

Построение и исследование дискретных динамических окрестностных моделей в Mathcad

Построение и исследование дискретных динамических окрестностных моделей в Mathcad

A discrete crack dynamics model of toughening in brittle polycrystalline material by crack deflection

This paper focuses on the study of the effect of the interfacial strength of grain boundaries and elliptical inclusions on crack path deflection. The method is developed to channel a crack into a toughening configuration (arrays of elliptical holes and inclusions are considered) in order to obtain the optimised microstructure required to enhance fracture toughness through different mechanisms. The proposed technique is shown to reproduce experimental crack propagation paths in various configurations and is capable of capturing the effect of that variation of the GB and the inclusion interfacial strength; it provides a powerful tool to understand the interplay between microstructural features and improve materials performance.

Prediction of airway resistance in panel cave mines using a discrete and continuum model

The configuration of an airway (or production drift) in panel cave mines is different from the typical (straight) mine airway designs. The drawpoints are connected to the airway (cross-cuts), which allows airflow from the cave into the airway or air loss from the airway into the cave due to the ventilation approach and cave porosity. These affect airflow in the production drifts, but it is difficult to investigate these conditions from field or laboratory scaled studies. Therefore, this study develops discrete and continuum computational fluid dynamics (CFD) models to study the effects of the ventilation approach and cave porosity on the airway resistance. Our findings show that: with active undercut ventilation, a unique resistance model is required for the airway in panel cave mines; and an increase in cave porosity decreases the drift’s resistance. These findings provide essential tools for a panel cave ventilation design.

Epidemiological characteristics of pulmonary tuberculosis in mainland China from 2004 to 2015: a model-based analysis

BackgroundWe used data released by the government to analyze the epidemiological distribution of pulmonary tuberculosis in mainland China from 2004 to 2015, in order to provide a deeper understanding of trends in the epidemiology of pulmonary tuberculosis in China and a theoretical basis to assess the effectiveness of government interventions and develop more targeted prevention and control strategies.MethodsA discrete dynamic model was designed based on the epidemiological characteristics of pulmonary tuberculosis and fitted to data published by the government to estimate changes in indicators such as adequate contact rate, prevalence of non-treated pulmonary tuberculosis (abbreviated as prevalence), and infection rate. Finally, we performed sensitivity analyses of the effects of parameters on the population infection rate.ResultsThe epidemiological features of pulmonary tuberculosis in China include a pattern of seasonal fluctuations, with the highest rates of infection in autumn and winter. The adequate contact rate has increased slightly from an average of 0.12/month in 2010 to an average of 0.21/month in 2015. The prevalence in the population has continued to decrease from 3.4% in early 2004 to 1.7% in late 2015. The Mycobacterium tuberculosis (M. tuberculosis) infection rate in the population decreased gradually from 42.3% at the beginning of 2004 to 36.7% at the end of 2015. The actual number of new infections gradually decreased from 1,300,000/year in 2010 to 1,100,000/year in 2015. The actual number of new patients each year has been relatively stable since 2010 and remains at approximately 2,600,000/year.ConclusionsThe population prevalence and the M. tuberculosis infection rate have decreased year by year since 2004, indicating that the tuberculosis epidemic in China has been effectively controlled. However, pulmonary tuberculosis has become increasingly contagious since 2010. China should focus on the prevention and control of pulmonary tuberculosis during autumn and winter.

Event mining and timeliness analysis from heterogeneous news streams

News documents published online represent an important source of information that can be used for event detection and tracking as well as for analyzing the temporal publishing relationships among different news streams.In this paper, we describe our research on detecting, tracking, and predicting events from multiple news streams. We also analyze the temporal publishing patterns of newswires on different platforms and their timeliness in reporting the events. First, we present an approach based on discrete dynamic topic modeling and Hidden Markov Model for event detection and tracking. Then, we predict the events that would persist in the next time slice, which can be important for forecasting facts that would be popular in the future. We leverage the detected events for clustering news documents according to the events they describe. This allows us to determine which newswires published news about an event and to analyze their temporal ordering in reporting events. Finally, we propose two scoring functions for ranking the newswires based on their timeliness.We tested our methodologies on different collections of news articles and tweets. Moreover, we built a collection of heterogeneous news documents with event-document labels which were manually assessed using crowdsourcing. Experimental results showed that, compared to the traditional dynamic topic model, our approach is able to timely detect emerging topics (events). Overall, we could register an event coverage of about 90% w.r.t. the pool of labeled events. The evolution of events is captured by event chains which are highly coherent (0.76) and informative (0.60) allowing to effectively reconstruct the stories. Furthermore, the event-based clustering of news documents has a good trade-off of precision and recall (F-score = 0.83) and the topic keywords provide a semantic description of the events represented by the clusters. Concerning our analysis on the temporal publishing relationships among news streams, we could observe interesting patterns on the usage of the different platforms, for example, some newswires still favor their own official websites, while others tend to publish more timely on Twitter.

Estimation of the world economic system stability from 1963 to 2013 by using a discrete dynamic model

Estimation of the world economic system stability from 1963 to 2013 by using a discrete dynamic model

Simulation of continuous flows with discrete models

The vast majority of heat and power processes include the motion of significant amounts of gases and liq-uids. This makes it important and quite urgent to develop approaches for computer simulation and visualiza-tion of continuum flows in technological devices and pipelines. A whole set of new approaches to mathematical modelling of continuum flows has been recently developed. The most common one is using discrete mathematical models for these purposes. Discrete approaches can simplify modeling procedures in cases where traditional methods require complex time-consuming calculations. At the same time, correct-ness of description of various flow regimes by the discrete methods is often questioned. The second problem of the mentioned models is a large-scale transition from model discrete parameters to generally accepted macroscopic characteristics of flows. The purpose of this work is to determine continuous flow regimes that can be correctly described by certain models. The paper considers discrete dynamic models in the form of lattice gases. A continuum in this case is represented by a set of particles moving only in allowed directions. Despite certain limitations, there is solid evidence that lattice gases quite successfully describe a whole range of hydrodynamic phenomena, and the obtained results do not contradict the generally accepted views on the physical nature of continuum motion processes. The paper describes approaches that allow estimating flow parameters using generally accepted macroscopic indicators. It also studies possible application areas of lattice gas models using the motion of virtual particles on a spatial lattice (HPP and FHP models) and the model based on the discrete analogue of the Boltzmann equation (LBM model) to simulate and visualize continuum flows. The obtained data are in good agreement with the generally accepted results and do not contradict the provisions of classical hydrodynamics. The paper shows that the models considering particle collisions (HPP and FHP) are applicable to describing gas flows in laminar regimes. The LBM model should be considered to be more correct for simulation and visualization of real fluid flows.

Accuracy of incidental dynamic analysis of mobile elevating work platforms

This paper presents the results of a study into the dynamic behaviour of a support structure of a mobile elevating work platform. The vibrations of the mechanical system of the observed structure are examined analytically, numerically, and experimentally. Within the analytical examination, a simple mathematical model is developed to describe free and forced vibrations. The dynamic analysis of the mechanical system is conducted using a discrete dynamic model with a reduced number of vibrational degrees of freedom. On the basis of the expression for the system energy, and by applying Lagrange\'s equations of the second kind, differential equations are derived for system vibrations, frequencies are determined, and the laws of forced platform vibration are established. At the same time, a nonlinear FEM model is developed and the laws of free and forced vibration are determined. The experimental and numerical part of the study deal with the examination of the real structure in extreme conditions, taking into account: the lowest eigenfrequency, forced actions that could endanger the general stability, the maximal amplitudes, and the acceleration of the work platform. The obtained analytical and numerical results are compared with the experiments. The experimental verification points to the adverse behaviour of the platform in excitation cases – swaying. In such a situation, even a relatively small physical force can lead to unacceptably high amplitudes of displacement and acceleration – exceeding the usual work values.

Optimal positions of translational vibration absorbers in vibroisolation of mechanical press

The paper deals with the problem of optimizing the positions of dynamic vibration absorbers in a mechanical press subjected to harmonic excitation force. Assuming flat motion of a rigid body and small vibrations, a discrete linear dynamic model of the press with absorbers is constructed. Using the results of numerical calculations, the optimal positions of the single or two vibration absorbers tuned to the excitation frequency, for different direction of excitation force, are obtained.

Global stability of discrete virus dynamics models with humoural immunity and latency

This paper studies the global stability of discrete-time viral infection models with humoural immunity. We consider both latently and actively infected cells. We study also a model with general production and clearance rates of all compartments as well as general incidence rate of infection. We use nonstandard finite difference method to discretize the continuous-time models. The positivity and boundedness of solutions of the discrete models are established. We establish by using Lyapunov method, the global stability of equilibria in terms of the basic reproduction number and the humoural immune response activation number . The results signify that the infection dies out if . Moreover, the infection persists with inactive immune response if and with active immune response if . We illustrate our theoretical results by using numerical simulations.

New non-destructive dynamic tensile testing of prestressing fine-rolled screw-threaded steel bars

This paper presents a new non-destructive dynamic tensile test for fine-rolled screw-threaded steel bars (FSSBs) in prestressed concrete box-girder bridges. In this study, the anchorage nut and anchor plate are connected by a coupling spring, so are the steel bar and nut threads. A discrete dynamic model of a spring–mass system was therefore established to evaluate the bending vibration of the anchorage system. The tensile force in prestressing FSSBs can be determined indirectly using the measured natural frequency of the exposed section. Based on the force transmission characteristics of threads, a frequency correction equation is proposed to correct the test error in the tensile force. The laboratory model and field tests of multiple bridges show that the proposed test method for tensile force is feasible and practical. The proposed tension test method is rapid, non-destructive, and can be used repeatedly. It has no impact on the construction and offers potential wide applications. The study results are significant in terms of the testing and analysis of the induced tensions in mechanical components and similar structures of civil engineering.