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In a previous paper (Feng et al., J. Differential Equations (2023)), we studied a seasonally interactive model between closed seasons and open seasons with Michaelis-Menten type harvesting, in which we assumed that the harvesting quantity was relatively large (0 < κ = l G c E < 1) and obtained a length threshold of the closed season T ¯ ⁎ depending on the harvesting parameter and the seasonal fluctuation period. It was shown that the origin is globally asymptotically stable if and only if T ¯ ≤ T ¯ ⁎ , and there exists a unique globally asymptotically stable T -periodic solution if and only if T ¯ > T ¯ ⁎. In this paper, we continue to investigate the periodic dynamics of this model when the harvesting quantity is relatively small (κ = l G c E ≥ 1). By finding another smaller length threshold T ¯ ⁎ ∈ (0 , T ¯ ⁎) , we determine the number of periodic solutions and study their stability, which imply the occurrence of bifurcation of periodic solutions. Our results demonstrate that designing the closed harvesting season properly can prevent the species from extinction. Moreover, by comparing with the continuous harvesting model and combining the results in our previous paper and this article, we provide a complete understanding on the global dynamics for the periodic switching model. Some numerical simulations are also carried out to illustrate the theoretical results. [ABSTRACT FROM AUTHOR]

This paper is devoted to a bistable system for calcium buffering. We first prove two kinds of stability of diverging traveling fronts of the degenerate system (All buffers do not diffuse): the local C 0 -norm stability and the asymptotic stability. In particular, as for asymptotic stability, we prove a Liouville-type result by the sliding method, and then use the truncation technique to study the long-time behavior of diverging wave like solution. These stabilities imply that, under suitable conditions on the initial data, the solution locally uniformly approaches to the high equilibrium state (1 , b 2). Then, by examining the behavior of solutions with one-parameter family of initial data, we show that the parameter-dependent solutions can be divided into three categories: convergence to the basal equilibrium state (0 , b 0) for small parameter values, convergence to the high equilibrium state (1 , b 2) for large parameter values, whereas neither of these behaviors occurs for intermediate parameter values. We refer to such phenomenon as threshold phenomenon. These intermediate parameter values are called threshold values, and the corresponding solutions are called threshold solutions. At the end of the paper, we present some important properties of the threshold solution and provide some numerical simulations. [ABSTRACT FROM AUTHOR]

This paper is devoted to the study of spreading properties and traveling wave solutions for a vector-host disease system, which models the invasion of vectors and hosts to a new habitat. Combining the uniform persistence idea from dynamical systems with the properties of the corresponding entire solutions, we investigate the propagation phenomena in two different cases: (1) fast susceptible vector; (2) slow susceptible vector when the disease spreads. It turns out that in the former case, the susceptible vector may spread faster than the infected vector and host under appropriate conditions, which leads to multi-front spreading with different speeds; while in the latter case, the infected vector and host always catch up with the susceptible vector, and they spread at the same speed. We further obtain the existence and nonexistence of traveling wave solutions connecting zero to the endemic equilibrium. We also conduct numerical simulations to illustrate our analytic results. [ABSTRACT FROM AUTHOR]

This paper demonstrates a theoretical and experimental study on a universal vibro-impact system with bidirectional drift. With a dedicated experimental rig that is able to verify numerical simulations, the system has revealed various bifurcations from a piecewise-smooth dynamical model involving impact and dry friction. This experimental rig with a two-sided constraint is designed with adjustable configurations which can be used for experimental testing of versatile piecewise-smooth dynamical systems, e.g., the impact oscillator, the drifting oscillator and the capsule system. It is able to be customised to alter different system parameters, such as friction, number of constraints, mass ratio, impact gap and constraint stiffness, for developing and testing various control strategies. In this paper we particularly studied several types of bifurcations from our preliminary experimental results and discussed the dynamical responses of the system under different excitation frequencies and amplitudes. It was found that with a higher excitation frequency and amplitude, the vibro-impact dynamics on both ends of the constraints could result in a large amount of uncertainties, thus bi-stable and chaotic motions are likely to be observed. While being unstable, the system runs with a relatively high energy efficiency in this configuration. [Display omitted] • An experimental rig with a two-sided constraint and bidirectional drift is studied. • The rig is designed with adjustable configurations for testing versatile systems. • System parameters are identified and verified by numerical simulations. • Grazing and sliding bifurcations, bi-stability and chaotic motions are studied. • Control parameters that cause instability may lead to high energy efficiency. [ABSTRACT FROM AUTHOR]

As we have known that it is impossible to attenuate the vibration displacement of the floating-slab depending on a strong stiffness and to improve the low-frequency vibration isolation performance of the floating-slab track (FST) depending on a soft stiffness simultaneously in engineering. In this paper, we propose a novel method to solve the paradox by introducing a "Hardening-First-Then-Softening" (HFTS) design based upon the energy distribution of wheel-rail loads to formulate a model of nonlinear floating-slab isolator. The average procedure is employed to analyze the vibration isolation ability of the isolator with parameters taken from a metro line load excitation. A simulation model of train-FST-tunnel with HFTS isolator is constructed to study the dynamic behaviors of the system. The numerical simulations show the significant suppression of displacement response of floating-slab and Z weighted acceleration vibration level of the tunnel. The results presented herein this paper provide a scheme to solve the strict requirements of displacement suppression and the vibration isolation which is of beneficial to steady and silent urban rail transit. [ABSTRACT FROM AUTHOR]

Observation missions of meteoroids entering the Earth's atmosphere are conducted regularly. Meanwhile a method to replicate the flight in a ground test facilities has been established. However, numerical simulations with subsequent comparison of the spectroscopic data, on the other hand, are not yet widely used in this field. This is mainly due to the complex flow environment, which includes not only non-equilibrium radiation, but also the outgassing of species from the meteoroid that do not enter the shock since they have only the thermal velocity of the wall without macroscopic flow and therefore cannot heat up as much as the other species. This paper presents a numerical approach to replicate experimental measurements. The Direct Simulation Monte Carlo (DSMC) method is used and bi-directionally coupled with a radiation solver to simulate the atmospheric entry in 80 km of an iron meteorite with a diameter of 38 mm. The paper provides information and references on the numerical models used, the challenges encountered, and the simulation results. The study shows that the simulation models are well-suited to handle the non-equilibrium effects of meteorite entry and show good agreement with the experimental measurements. • Complete non-equilibrium simulation of a meteoroid with a gas kinetic solver. • First coupled radiative flow simulation of a meteoroid. • First successful numerical reproduction of a measured meteor spectrum by simulation. [ABSTRACT FROM AUTHOR]

Refuge provides an important mechanism for preserving many ecosystems. Prey refuges directly benefit prey but also indirectly benefit predators in the long term. In this paper, we consider the complex dynamics and bifurcations in Holling-Tanner model with generalist predator and prey refuge. It is shown that the model admits a nilpotent cusp or focus of codimension 3, a nilpotent elliptic singularity of codimension at least 4, and a weak focus with order at least 3 for different parameter values. As the parameters vary, the model can undergo three types degenerate Bogdanov-Takens bifurcations of codimension 3 (cusp, focus and elliptic cases), and degenerate Hopf bifurcation of codimension 3. The system can exhibit complex dynamics, such as multiple coexistent periodic orbits and homoclinic loops. Moreover, our results indicate that the constant prey refuge prevents prey extinction and causes global coexistence. A preeminent finding is that refuge can induce a stable, large-amplitude limit cycle enclosing one or three positive steady states. Numerical simulations are provided to illustrate and complement our theoretical results. [ABSTRACT FROM AUTHOR]

Existence, uniqueness and stability of forced pulsating waves as well as gap formation of reaction diffusion models in a shifting habitat are challenging problems in the field of propagation dynamics. In this paper, we design to tackle these problems for a time periodic Lotka-Volterra competition system. By using alternatively-coupling upper-lower solution method, we establish the existence of forced pulsating traveling wave, as long as the shifting speed falls in a finite interval where the end points are obtained from KPP-Fisher speeds. The asymptotic behaviors of the forced pulsating traveling wave are derived and this helps us show that this wave is unique. Moreover in the Lyapunov sense, the stability of the forced pulsating wave is also studied. Finally, when the forced speed is beyond the finite interval, gap formation is investigated theoretically and illustrated further by numerical simulations. [ABSTRACT FROM AUTHOR]

In this paper, we propose an extended model for the numerical simulation of evaporating droplets within the framework of interface capturing or interface tracking methods. Most existing works make several limiting assumptions that need to be overcome for a more accurate description of the evaporation of droplets. In particular, the variations of several physical variables with local temperature and mass fraction fields must be accounted for in order to perform more realistic computations. While taking into account the variations of some of these physical properties, as viscosity, seems rather obvious, variations of other variables, as density and surface tension, involve additional source terms in the fundamental equations for which a suitable discretization must be developed. The paper presents a numerical strategy to account for such an extended model along with several original test-cases allowing to demonstrate both the accuracy of the proposed numerical schemes and the strong interest in developing such an extended model for the simulation of droplet evaporation. In particular, the impact of thermo-capillary convection will be highlighted on the vapor film thickness between a superheated wall and a static Leidenfrost droplet levitating above this wall. • An extended model is proposed for the direct numerical simulation of evaporating droplets. • A suitable numerical framework is developed to solve this extended model. • Novel benchmarks are proposed to validate the extended model and the proposed numerical approach. • A significant impact of the density variations on the Nusselt number is reported for a moving and evaporating droplet. • A strong effect of the Marangoni convection is also reported for Leidenfrost droplets. [ABSTRACT FROM AUTHOR]

Projection methods are applicable in many fields. It is a natural and practical approach to devise the invariant-preserving schemes for conservative systems. The idea is to project the solution of any underlying numerical scheme onto the manifold determined by the invariant, and this process will be referred to as the projection integrator. Generally, the projection integrator chooses the gradient of invariant as its projection direction and has the same order as the underlying method. In this paper, we propose a different projection direction to construct a new projection integrator whose order is higher than the underlying method. According to this novel direction, we further summarize high-order projection integrators with superconvergence and rigorously prove the truncation error by utilizing the linear integral method as a central tool. Apart from the invariant-preserving property, symmetry is an important geometric property for reversible differential equations. The design and analysis of another high-order projection integrators with symmetry and superconvergence are also presented in this paper. Numerical experiments are provided to verify our theoretical results and illustrate that our proposed projection integrators have superior behaviors in a long time numerical simulation. [ABSTRACT FROM AUTHOR]

Structured triacylglycerols with 1,3-dioleoyl-2-palmitoylglycerol (OPO) have many health benefits for infants. In this paper, tripalmitin (PPP) and oleic acid (OA) were used as raw materials, the method of magnetic fluidized bed and immobilized lipase was used in the synthesis reaction of OPO. Reaction parameters in the fluidized bed were simulated by computer. The results showed that flow rate of 0.0023 m/s and magnetic field strength of 0.021 T were the optimal conditions for the synthesis of OPO in the magnetic fluidized bed. Under the same conditions, OPO content in the magnetic fluidized bed was 45.79%, which was 3.11% higher than batch reaction. After 7 times of reuse, the enzyme activity in fluidized bed was 81.75%, which was 10.7% higher than that of the batch reaction. This study may provide an efficient and more economical method for OPO production in the future. • Magnetic fluidized bed and computer simulation were used in the OPO synthesis. • Content of Sn-2 palmitic acid in magnetic fluidized bed was 85.39 %, OPO content was 45.79 %. • The content of OPO in the magnetic fluidized bed product was 7.3% higher than in the common reaction. • Magnetic fluidized bed can better retain the activity of immobilized enzymes. [ABSTRACT FROM AUTHOR]

[Display omitted] The paper proposes to identify the parameters of linear dynamic models based on the original implementation of least absolute deviation estimators. It is known that the object estimation procedures synthesized in the sense of the least sum of absolute prediction errors are particularly resistant to occasional outliers and gaps in the analyzed system data series, while the classical least squares procedure unfortunately becomes of little use for reliably identifying systems in the presence of destructive measurement errors. Bearing in mind that the classic task of minimizing the quality functional of absolute deviations encounters fundamental analytical problems, it is proposed to use a dedicated iterative estimator for off-line evaluation of the parameters of the analyzed process. In addition, a simplified recursive version of the absolute deviation estimation procedure was developed, which allows for practical on-line tracking of the evolution of variable parameters of non-stationary systems. Importantly, a novel refinement of the discussed absolute deviation estimators was proposed to effectively overcome some inconvenient numerical effects. We also present an interesting comparison of the improved (by non-linear modification) iterative absolute-deviation estimator with the classical Gauss-Newton gradient algorithm, which leads to constructive conclusions. Finally, using computer simulations, the operation of the developed iterative and recursive estimators minimizing the absolute deviation is illustrated. The work ends with an indication of directions for further research. [ABSTRACT FROM AUTHOR]

In this paper, we present a computational framework based on fully Eulerian models for fluid–structure interaction for the numerical simulation of biological capsules. The flexibility of such models, given by the Eulerian treatment of the interface and deformations, allows us to easily deal with the large deformations experienced by the capsule. The modeling of the membrane is based on a full membrane elasticity Eulerian model that is capable of capturing both area and shear variations thanks to the so-called backward characteristics. In the validation section several test cases are presented with the goal of comparing our results to others present in the literature. In this part, the comparisons are done with different well-known configurations (capsule in shear flow and square-section channel), and by deepening the effect of the elastic constitutive law and capillary number on the membrane dynamics. Finally, to show the potential of this framework we introduce a new test case that describes the relaxation of a capsule in an opening channel. In order to increase the challenges of this test we study the influence of an internal nucleus, modeled as a hyperelastic solid, on the membrane evolution. Several numerical simulations of a 3D relaxation phenomenon are presented to provide characteristic shapes and curves related to the capsule deformations, while also modifying size and stiffness parameter of the nucleus. [ABSTRACT FROM AUTHOR]

• A large-scale benchmark dataset with airfoil mesh samples. • A lightweight deep neural network MQNet for mesh quality evaluation. • A MQNet-based meshing workflow for high-quality airfoil mesh generation. Evaluating mesh quality before solving is crucially important for error control in the numerical simulation of airfoils. Traditional mesh quality metrics are used to identify distorted mesh elements by analyzing their geometric shape information like angles and edges. However, these metrics fail to recognize numerical errors stemming from quality attributes such as improper mesh density or distribution. This deficiency has imposed a burden on intensive manual re-evaluation, which heavily increases the meshing cost. In this paper, we introduce deep neural networks to airfoil mesh quality evaluation to improve its automation and efficiency. Specifically, we propose a neural network-based evaluation model, MQNet, accompanied by the first large-scale mesh benchmark dataset, AirfoilSet. MQNet is trained on the dataset to learn the quality-related attributes including mesh orthogonality, smoothness, and density. Thereafter, the trained network can be used as a black box to automatically evaluate and output the overall quality of the airfoil mesh. To demonstrate the effectiveness and generalization behaviors of the proposed network, we establish an MQNet-based mesh generation workflow. Experimental results show that MQNet is small and accurate. It outperforms widely-used neural networks and can be a useful tool to guide the high-quality mesh generation process with minimal user intervention. [ABSTRACT FROM AUTHOR]

Highlights • We have corrected the paper in order to present more clearly the experimental results and also to comment more the simulations done for the present Boolean model. • As demanded by reviewers, we have added a short presentation of the R. Thomas' theory, and also a recall of the earlier Boolean model proposed with him for the experiments of stimulation of Bidens pilosus. • Eventually, we have tried to present the perspectives of a hybrid approach from the continuous model previously proposed for Bidens. Abstract This paper presents a new model of memory functions in plants, which improves the previous approaches done by René Thomas and colleagues. We have decomposed the plant memory processing into three main functions: learning, storing and recalling. We propose as main mechanism for these three functions the occurrence of a calcium wave consecutive to an environmental stimulus, followed by the activation of specific genes and proteins changing their phosphorylated state. Feedback is ensured by Calcium Dependent Protein Kinases and oxidative phosphorylation. [ABSTRACT FROM AUTHOR]

Highlights • Numerical simulation method of ultrasonic propagation in flow of risers was set up. • Time domain diagram of received signals was analyzed. • Cross-correlation function was used to quantitatively analyze the received signals. • The method can be used as an effective supplement to the experiment. Abstract The ultrasonic transmission monitoring in risers is a promising method for the early detection of gas kick in deepwater drilling. It is difficult to obtain satisfactory results using only theoretical calculation because the ultrasonic wave propagation in the multiphase flow in risers is very complicated. In addition, the key parameters such as bubble shape and void fraction of two-phase flow are hard to be accurately controlled and measured. In view of the above-mentioned facts, this paper aims to analyze the principle and physical model of ultrasonic monitoring of gas kick in risers, and to establish a numerical simulation model based on COMSOL platform. Through an analysis of the numerical simulation results, it was found that the time domain diagram of the received signals contains longitudinal wave, transverse wave, surface wave and coda wave. The cross-correlation function was used to quantitatively analyze the waveform of the received signals under different void fraction conditions. It also suggested that the direct wave was insensitive to the void fraction while the coda wave was sensitive to the void fraction, which was verified through frequency domain analysis. By establishing the experimental system, the attenuation coefficient was used to verify the numerical simulation results. After comparing and analyzing data, this paper argued that the numerical simulation method established in the project can be used as an effective supplement to experiments, and it can be used to calculate and analyze the ultrasonic propagation and attenuation under conditions, such as different bubble sizes and densities, and bubble non-uniform distribution, which can not be accurately and quantitatively measured or controlled in the experiments. [ABSTRACT FROM AUTHOR]

Monitoring the condition of the infrastructure based on measurements coming from in-service trains is a recent trend in the policies of railway infrastructure managers and is seen as a major factor to reduce maintenance costs retaining the present levels of passengers’ ride comfort and availability of the lines. Aim of this paper is to develop and assess model-based methods for the identification of geometric track irregularities from acceleration measurements taken on-board vehicles travelling on the track. In particular, the paper focusses on the identification of lateral alignment irregularities, a yet unsolved problem which turns out to be much more demanding compared to the identification of longitudinal level irregularities due to the relative wheel-rail motion in lateral direction which occurs on account of the peculiar geometry of wheel-rail contact. The paper presents three different approaches to the estimation of the lateral and cross-level track irregularities, one defined in the frequency domain and two in the time domain. For each method, an assessment is performed based on numerical experiments in which virtual measurements from vehicle-mounted sensors are obtained by means of numerical simulations performed using a multi-body model of a railway vehicle. For the method defined in the frequency domain, a first application to line measurements is presented. [ABSTRACT FROM AUTHOR]

Highlights • Multi-controller coordinated deployment problem in software defined optical networks is studied in this paper. • A load balancing strategy named switch migration based controller placement algorithm (SMBCP) is proposed for multi-controller deployment. • Simulation results show SMBCP algorithm can significantly improve the load balancing and reduce the cost of switch migration. Abstract In software defined optical networks (SDON), a single controller can hardly manage all the optical devices especially in the large-scale networks, while multiple controllers deployed in the network can solve it. Recently, more and more attention has been paid to the multi-controller architecture, and the deployment of controllers is an important issue in large software defined optical networks. However, the existing architectures focus on static mapping of controllers and switches and do not consider load balance among different controllers. It is worth further studying the cooperation of multiple controllers. This paper presents a multi-controller coordinated deployment strategy (Switch Migration Based Controller Placement, SMBCP) based on load balancing. Simulation results show that SMBCP can significantly reduce the load difference among different controllers in SDON and reduce the migration cost of switches, thus improving the load balance of the controller. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we will investigate the approximations of inverse moments for double-indexed weighted sums of random variables under sub-linear expectations. The asymptotic approximations of inverse moments and the convergence rate of approximations are established under the meaning of upper expectation E ˆ and the lower expectation ε ˆ , respectively. Moreover, we carry out some simulations to verify the validity of our theoretical results. The results obtained in the paper improve and extend the corresponding ones of Yang et al. [24] from independent random variables in the classical probability space to END random variables in sub-linear expectation space. [ABSTRACT FROM AUTHOR]

In this paper, we first propose a reaction–diffusion waterborne pathogen model with general incidence rate, incorporating both direct and indirect transmission pathways. Then, using the basic reproduction number we investigate the global dynamical behaviors of the continuous model. By nonstandard finite difference scheme, we derive a discrete counterpart of the continuous model. Then, the global properties of the discretized model are investigated. Finally, we conclude the paper by an example and numerical simulations. [ABSTRACT FROM AUTHOR]

This paper investigates the use of non-linear structural dynamics computational models with multiple levels of fidelity for the calibration of input-dependent model parameters. Non-linear behavior complicates the calibration of model parameters that are input-dependent (i.e., functions of temperature, loading, etc.). Different types of models may also be available for the estimation of unmeasured system properties, with different levels of physics fidelity, mesh resolution and boundary condition assumptions. To infer these system properties, Bayesian calibration can be used to combine information from multiple sources (such as experimental data and prior knowledge) and comprehensively quantify the uncertainty in the model parameters. Estimating the posterior distributions is done using Markov Chain Monte Carlo sampling, which requires a large number of computations, thus making the use of a high-fidelity model for calibration prohibitively expensive. On the other hand, use of a low-fidelity model could lead to significant error in calibration and prediction. Therefore, this paper pursues a multi-fidelity approach for input-dependent model parameter calibration with a surrogate of the low-fidelity model corrected using higher fidelity simulation data. The effects of non-linear behavior and input-dependence of model parameters and measurements are systematically organized and distinguished using a Bayesian network. The methodology is illustrated with a curved panel, subjected to acoustic and thermal loading, where the damping properties of the panel could be functions of the acoustic loading and temperature magnitudes. Two models (a frequency response analysis and a full time history analysis) are combined to estimate the damping characteristics of the panel. The effect of the temperature on the performance of the strain gages and therefore on the calibration results is also studied. [ABSTRACT FROM AUTHOR]

In this paper, we mainly study the propagation properties of solutions of the predator-prey system with nonlocal dispersal. More specifically, we explored the spreading speeds of the predator and the prey in two different situations, namely, the predator spreads faster than the prey and the predator spreads slower than the prey. The main difficulty lies in the fact that the comparison principle cannot be used for the predator-prey system. We use the comparison principle of the scalar equation and the method of upper and lower solutions to prove the results. In addition, we establish the comparison principle of nonlocal dispersal equations in space and time dependent environment. We conclude that the predator and the prey will eventually coexist by constructing a suitable Lyapunov functional. Finally, we use numerical simulations to illustrate the results. [ABSTRACT FROM AUTHOR]

In this paper, we revisit the Holling-Tanner model with constant-yield prey harvesting. It is shown that the highest codimension of a nilpotent cusp is 4, and the model can undergo degenerate Bogdanov-Takens bifurcation of codimension 4. Moreover, when the model has a center-type equilibrium, we show that it is a weak focus with order at least 3 and at most 4, and the model can exhibit Hopf bifurcation of codimension 3. Some algebraic methods including resultant elimination and pseudo-division are used to solve the semi-algebraic varieties of normal form coefficients or focal values. Our results indicate that constant-yield prey harvesting can cause not only richer dynamics and bifurcations, but also the coextinction of both populations with some positive initial densities. Finally, numerical simulations, including the coexistence of limit cycle and homoclinic cycle, and three limit cycles, are presented to illustrate the theoretical results. [ABSTRACT FROM AUTHOR]

Computer architecture courses typically include lab sessions to reinforce, from a practical perspective, concepts and architectural mechanisms studied in lectures. Lab sessions are mainly based on simulation frameworks because they benefit learning. Reading the source code that models certain processor mechanisms allows students to acquire a sound knowledge of how hardware works. Unfortunately, simulators that model current multicore processors are getting more and more complex, which lengthens the learning phase and complicates their use in time-bounded lab sessions. In this paper, we propose a new approach that complements the use of simulation frameworks in lab sessions of computer architecture courses. This approach is based on performing experiments on current commercial processors, where multiple hardware events related to the performance of the computer components under study are monitored. Then, students analyze the measured events and how they impact the overall performance. Such analysis motivates students and, not only helps reinforcing the theoretical concepts, but also increases their analysis skills. In this paper we present the methodology and scheduling framework that support the proposed approach and discuss five lab sessions, which can be applied in different courses, covering multiple computer architecture topics. [ABSTRACT FROM AUTHOR]

Flow-induced vibrations of heat-exchanger tubes are extensively studied in the nuclear industry for safety reasons. Adequate designs, such as anti-vibration bars in PWR steam generators, prevent excessive vibrations provided the tubes are well supported. Nevertheless, degraded situations where the tube/support gaps would widen, must also be considered. In such a case, the tubes become loosely supported and may exhibit vibro-impacting responses due to both turbulence and fluid–elastic coupling forces induced by the cross-flow. This paper deals with the predictive analysis of such a nonlinear situation, given the necessity of taking into account both the strong impact nonlinearity due to the gap and the linearized fluid–elastic forces. In time-domain numerical simulations, computation of flow-coupling forces defined in the frequency-domain is a delicate problem. We recently developed an approach based on a hybrid time–frequency method. In the present paper a more straightforward and effective technique, based on the convolution of a flow impulse response pre-computed from the frequency-domain coefficients, is developed. Illustrative results are presented and discussed, in connection with the previous hybrid method and with experiments. All results agree in a satisfactory manner, validating both computational methods, however the convolutional technique is faster than the hybrid method by two orders of magnitude. Finally, to highlight the subtle self-regulating frequency effect on the stabilization of such system, additional demonstrative computations are presented. [ABSTRACT FROM AUTHOR]

This paper aims to model the hydrodynamic forces on grids of perforated flat plates undergoing forced motions at three scales, namely steady (current), and combined low (wave) frequency and high (structural) frequency oscillatory motion. The intended application is the design and re-assessment of dynamically-responding offshore platforms. A recent set of experimental results by Santo et al. (2018c) is taken as the reference for comparison with the numerical predictions. A block of porous cells is used as a proxy to the grids of perforated plates in the numerical simulation, but with comparable resistance and added mass represented by equivalent Morison drag and inertia stresses both uniformly distributed over the porous cells. Both stresses are characterised by empirical force coefficients, F and C m ′ , which correspond to Morison drag, C d and inertia, C m coefficients, respectively. Using these two adjustable empirical parameters, the simulated forces compare reasonably well with the measured hydrodynamic forces on the grids, both in terms of peak forces as well as the complete force–time histories for most of the flow conditions tested in the experiments. This is particularly true when the amplitude of wave velocity is larger than that of current velocity, a representation of large waves in a small current which is realistic for the harsh ocean environment. The porous block model is capable of capturing the global large-scale wake structures, which are responsible for the reduction in fluid flow velocity and associated forces on a structure. The simulated forces however only exhibit slight force asymmetry, unlike the measured forces, because the local fine-scale wake structures are not represented in the numerical modelling. For the scale of the experiments used for the comparison, the contribution from these small-scale wake structures to the global hydrodynamic forces can be quite significant, in particular when the amplitude of wave velocity is comparable to that of current velocity. Overall, this paper demonstrates the versatility of the porous block modelling approach in capturing most of the dominant flow physics and reproducing almost all the experimental results. The generality of the approach allows straightforward extension to wider range of flow conditions including three-dimensional flow. [ABSTRACT FROM AUTHOR]

In this paper, delayed sub-optimal control based on partial-state feedback for flutter suppression system involving time-delay is investigated, and the effectiveness of the sub-optimal controller is compared with the optimal controller based on full-state feedback. Firstly, the aeroservoelastic (ASE) model of the flexible wing with control surfaces is given, and the method to dispose the time-delay in the control input is introduced. Then, the determination of the importance of each state in control feedback is studied using the second-order sensitivity of the performance index with respect to the control gain. Finally, the effectiveness of sub-optimal controller is compared with optimal controller through numerical simulations. Simulation results show that the importance of states can be effectively determined by the second-order sensitivity, and the delayed sub-optimal controller can achieve a control effect quite close to the delayed optimal controller. The order of the delayed suboptimal controller designed in this paper is lower, so it shows more engineering significance. [ABSTRACT FROM AUTHOR]

We consider a class of tumor growth models under the combined effects of density-dependent pressure and cell multiplication, with a free boundary model as its singular limit when the pressure-density relationship becomes highly nonlinear. In particular, the constitutive law connecting pressure p and density ρ is p ( ρ ) = m m − 1 ρ m − 1 , and when m ≫ 1 , the cell density ρ may evolve its support according to a pressure-driven geometric motion with sharp interface along its boundary. The nonlinearity and degeneracy in the diffusion bring great challenges in numerical simulations. Prior to the present paper, there is lack of standard mechanism to numerically capture the front propagation speed as m ≫ 1 . In this paper, we develop a numerical scheme based on a novel prediction-correction reformulation that can accurately approximate the front propagation even when the nonlinearity is extremely strong. We show that the semi-discrete scheme naturally connects to the free boundary limit equation as m → ∞ . With proper spatial discretization, the fully discrete scheme has improved stability, preserves positivity, and can be implemented without nonlinear solvers. Finally, extensive numerical examples in both one and two dimensions are provided to verify the claimed properties in various applications. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach to detect the milling chatter based on Variational Mode Decomposition (VMD) and energy entropy. VMD has already been employed in feature extraction from non-stationary signals. The parameters like number of modes (K) and the quadratic penalty (α) need to be selected empirically when raw signal is decomposed by VMD. Aimed at solving the problem how to select K and α, the automatic selection method of VMD’s based on kurtosis is proposed in this paper. When chatter occurs in the milling process, energy will be absorbed to chatter frequency bands. To detect the chatter frequency bands automatically, the chatter detection method based on energy entropy is presented. The vibration signal containing chatter frequency is simulated and three groups of experiments which represent three cutting conditions are conducted. To verify the effectiveness of method presented by this paper, chatter feather extraction has been successfully employed on simulation signals and experimental signals. The simulation and experimental results show that the proposed method can effectively detect the chatter. [ABSTRACT FROM AUTHOR]

This paper is concerned with the generation of a quiet space in a rectangular cavity using active wave control methodology. It is the purpose of this paper to present the wave filtering method for a rectangular cavity using multiple microphones and its application to an adaptive feedforward control system. Firstly, the transfer matrix method is introduced for describing the wave dynamics of the sound field, and then feedforward control laws for eliminating transmitted waves is derived. Furthermore, some numerical simulations are conducted that show the best possible result of active wave control. This is followed by the derivation of the wave filtering equations that indicates the structure of the wave filter. It is clarified that the wave filter consists of three portions; modal group filter, rearrangement filter and wave decomposition filter. Next, from a numerical point of view, the accuracy of the wave decomposition filter which is expressed as a function of frequency is investigated using condition numbers. Finally, an experiment on the adaptive feedforward control system using the wave filter is carried out, demonstrating that a quiet space is generated in the target space by the proposed method. [ABSTRACT FROM AUTHOR]

This paper addresses the coupled nonlinear Schr ö dinger equation (CNLSE) in monomode step-index in optical fibers which describes the nonlinear modulations of two monochromatic waves, whose group velocities are almost equal. A class of dark, bright, dark-bright and dark-singular optical solitary wave solutions of the model are constructed using the complex envelope function ansatz. Singular solitary waves are also retrieved as bye products of the in integration scheme. This naturally lead to some constraint conditions placed on the solitary wave parameters which must hold for the solitary waves to exist. The modulation instability (MI) analysis of the model is studied based on the standard linear-stability analysis. Numerical simulation and physical interpretations of the obtained results are demonstrated. It is hoped that the results reported in this paper can enrich the nonlinear dynamical behaviors of the CNLSE. [ABSTRACT FROM AUTHOR]

Mesh-based Eulerian and particle-based Lagrangian models are common computational fluid dynamics (CFD) tools for simulating wave-structure interactions. While Eulerian models are efficient in terms of computational time, they are limited in their ability to handle large interface discontinuities between two flows and complex structure motion responses. Conversely, Lagrangian models are suitable for such discontinuities and motion responses but can be computationally expensive. However, there is a lack of comprehensive discussion on the (dis)advantages of hybrid Eulerian-Lagrangian models, which have the potential to achieve both numerical efficiency and flexibility through a combined use of mesh and particles. This paper presents a comparative study of a hybrid Eulerian-Lagrangian Particle-In-Cell (PIC) model and the widely-used OpenFOAM model, applied to a variety of complex wave interactions with floating offshore renewable energy structures in both 2D and fully 3D domains. We found that both models demonstrate good performance in simulating complex floating structures. Additionally, it is the first time that the two models have been compared in parallel on the same computing facility, allowing us to directly show their computational efficiency. The PIC model has the advantage of using staggered grids, which enables it to achieve computational efficiency comparable to the pure mesh-based OpenFOAM. The findings of this study provide researchers and practitioners in the field of computational fluid dynamics with a clear understanding of the performance of the hybrid Eulerian-Lagrangian PIC model and OpenFOAM for simulating complex fluid-structure interaction problems. [ABSTRACT FROM AUTHOR]

• An approach is proposed for identification of bridge bending stiffness distribution using improved Gaussian peak function. • The improved Gaussian peak function allows for considering a wider range of stiffness variation models and thus is a general model. • The Levenberg-Marquardt (LM) method is proposed for parameter estimation and shows good robustness with different initial parameter values. • Numerical simulation and laboratory experiment are used to verify the effectiveness of the proposed method in identifying bridge bending stiffness distribution. Bridge damage and bending stiffness deterioration can lead to a decrease in the bearing capacity of a bridge, posing significant safety concerns. To ensure the safe operation of bridges, it is crucial to accurately identify bending stiffness deterioration and assess the bridge performance. The bridge influence line (IL), which reflects the deterioration of bending stiffness, was widely used in the assessment of bending stiffness deterioration. Existing IL-based methods mostly assume a uniform reduction in bending stiffness for identification. In reality, the deterioration of bridge bending stiffness is far more complex, which causes difficulty in accurately identifying the bending stiffness distribution using the uniform reduction model. This paper proposes a novel method for identifying bridge stiffness distribution using an improved Gaussian peak function model. The improved model incorporates additional parameters, allowing for considering a wider range of stiffness variation and thus addressing the limitations of traditional models. The parameters of the improved Gaussian peak function model are estimated by minimizing the residual between the predicted deflection influence line (DIL) and the actual DIL using the Levenberg-Marquardt (LM) algorithm. This approach enables the accurate identification of bending stiffness distribution without baseline information. Numerical simulation and laboratory experiment are used to verify the effectiveness of the proposed method in identifying bridge bending stiffness distribution. A comparison between the identified and actual bending stiffness distribution curves under various forms of damage assesses the applicability of the proposed method. [ABSTRACT FROM AUTHOR]

• A novel multi-extracting velocity-synchronous chirplet transform (MEVCT) for efficient and effective time–frequency analysis. • An adaptive chirp angle search method for improving computational efficiency and velocity synchronous basis accuracy. • A higher-order iterative extraction operator for eliminating the non-reassigned time–frequency points. • The improved IF accuracy and anti-noise capability of MEVCT provide ideal TFR for synchronous multi-component signals. • Demonstrated advantages of MEVCT by numerical simulations as well as experimental tests. In many engineering applications, the instantaneous frequency (IF) needs to be identified rapidly and precisely, especially in rotating machinery condition monitoring, where quasi-real-time analysis is a favorable option, and any error in shaft speed (identified from the instantaneous frequency) needs to be reduced to prevent it from accumulating with time. The modern time–frequency analysis (TFA) method provides a way for IF identification; however, sometimes, it still suffers from energy smearing and closely spaced frequency interference. In addition, many TFA methods based on the chirplet transform also present the problem of excessive computation when searching for the optimal parameters. To overcome these limitations, we propose the multi-extracting velocity-synchronous chirplet transform (MEVCT), an enhanced TFA method, in this paper. In the MEVCT, a refined chirp parameter search is developed first to reduce the computational cost while increasing time–frequency accuracy. Then, an iterative high-order IF estimator is constructed to allow the IF to achieve or approach the actual values even in highly nonlinear situations. After that, the obtained IF estimate is substituted into the simultaneous extraction operator to reduce energy dispersion further and eliminate non-reassigned points (NRPs). Simulated and experimental signal analyses demonstrate that MEVCT is able to eliminate NRPs completely. Furthermore, when handling synchronous multicomponent signals, the proposed method has higher IF accuracy with less computational cost and better anti-noise capability. [ABSTRACT FROM AUTHOR]

In this paper we present the experimental verification of the novel tuned mass damper which enables changes of inertance. Characteristic feature of the proposed device is the presence of special type of inerter. This inerter incorporates a continuously variable transmission that enables stepless changes of inertance. Thus, it enables to adjust the parameters of the damping device to the current forcing characteristic. In the paper we present and describe the experimental rig that consists of the massive main oscillator forced kinematically and the prototype of the investigated damper. We perform a series of dedicated experiments to characterize the device and asses its damping efficiency. Moreover, we perform numerical simulations using the simple mathematical model of investigated system. Comparing the numerical results and the experimental data we legitimize the model and demonstrate the capabilities of the investigated tuned mass damper. Presented results prove that the concept of the novel type of tuned mass damper can be realized and enable to confirm its main advantages. Investigated prototype device offers excellent damping efficiency in a wide range of forcing frequencies. [ABSTRACT FROM AUTHOR]

This paper is concerned with the stability of traveling waves for a Keller-Segel model with singular chemotactic term and zero chemo-attractant diffusion, where the model and the waves are established to explain the propagation of bacteria pulses along a capillary tube observed in Adler's experiment [1]. By applying the detailed spectral analysis, Evans function method and special transformations and combining with some numerical simulations, in some range of the parameters all the waves are shown to be spectrally stable in some exponentially weighted spaces, and in other range of parameters all the waves are shown to be unstable in any exponentially weighted spaces. The local well-posedness of the classical positive solution to the Cauchy problem of the model is also obtained by applying semigroup argument and some special transformations. [ABSTRACT FROM AUTHOR]

This paper is mainly concerned with the new types of entire solutions which are different from pulsating fronts of Lotka-Volterra competition systems with asymmetric dispersal in spatially periodic habitats. The asymmetry of kernel function leads to a great influence on the profile of pulsating fronts and the sign of wave speeds, which gives rise to the properties of the entire solution more complex and diverse. We first give a relationship between the critical speeds c ⁎ (ξ) and c ⁎ (− ξ) , corresponding to the minimal speeds of two pulsating fronts propagating in the direction of ξ and − ξ , respectively. Then, the exponential behavior of pulsating fronts as they approach their limiting states is obtained. Finally, by considering the interactions of two different pulsating fronts coming from two opposite/same directions and applying the super-/subsolutions techniques as well as the comparison principle, we establish the existence and various qualitative properties of some different types of entire solutions defined for all time and whole space. Moreover, we give some numerical simulations to describe intuitively these obtained entire solutions. [ABSTRACT FROM AUTHOR]

In this paper, we study a model for opinion dynamics where the influence weights of agents evolve in time via an equation which is coupled with the opinions' evolution. We explore the natural question of the large population limit with two approaches: the now classical mean-field limit and the more recent graph limit. After establishing the existence and uniqueness of solutions to the models that we will consider, we provide a rigorous mathematical justification for taking the graph limit in a general context. Then, establishing the key notion of indistinguishability , which is a necessary framework to consider the mean-field limit, we prove the subordination of the mean-field limit to the graph one in that context. This actually provides an alternative proof for the mean-field limit. We conclude by showing some numerical simulations to illustrate our results. [ABSTRACT FROM AUTHOR]

The paper extends to moist-precipitating dynamics a recently documented high-performance finite-volume module (FVM) for simulating global all-scale atmospheric flows (Smolarkiewicz et al., 2016) [62] . The thrust of the paper is a seamless coupling of the conservation laws for moist variables engendered by cloud physics with the semi-implicit, non-oscillatory forward-in-time integrators proven for dry dynamics of FVM. The representation of the water substance and the associated processes in weather and climate models can vary widely in formulation details and complexity levels. The representation adopted for this paper assumes a canonical “warm-rain” bulk microphysics parametrisation, recognised for its minimal physical intricacy while accounting for the essential mathematical complexity of cloud-resolving models. A key feature of the presented numerical approach is global conservation of the water substance to machine precision—implied by the local conservativeness and positivity preservation of the numerics—for all water species including water vapour, cloud water, and precipitation. The moist formulation assumes the compressible Euler equations as default, but includes reduced anelastic equations as an option. The theoretical considerations are illustrated with a benchmark simulation of a tornadic thunderstorm on a reduced size planet, supported with a series of numerical experiments addressing the accuracy of the associated water budget. [ABSTRACT FROM AUTHOR]

The paper presents a comparative study between symmetric and asymmetric straggle architecture, where asymmetric nature is observed by considering straggle in source and drain side alternatively by using the data obtained from 2D numerical simulator Sentaurus TCAD. The analog parameters such as the transconductance (g m ), the gain per unit current (g m /I ds )and the intrinsic gain (g m R o ) has been analyzed. RF parameters such as intrinsic gate to source and gate to drain capacitances C gs and C gd , intrinsic gate to source and gate to drain resistances R gs and R gd , the transport delay τ m , the unity gain cut off frequency (f T ) and the maximum frequency of oscillation (f max ) are also computed using the Non Quasi Static(NQS) approach. The RF feasibility has also been scrutinized with the help of linearity analysis and Harmonic Distortion (HD). The Second and Third order HD (HD2 and HD3) and Total HD(THD) have been analyzed to evaluate distortion performance. The circuit performance is also analyzed by using the devices as a driver MOSFET in a single stage amplifier circuit whose dc performance as well as small signal gain is evaluated and Gain Bandwidth Product (GBW) is also calculated in this paper. [ABSTRACT FROM AUTHOR]

The work herein proposes the use of the data-driven Loewner-framework for reduced order modeling as applied to dynamic Finite Element Models (FEM) of thermally morphing structures. The Loewner-based modeling approach is computationally efficient and accurately constructs reduced models using analytical output data from a FEM. This paper details the two-step process proposed in the Loewner approach. First, a random vibration FEM simulation is used as the input for the development of a Single Input Single Output (SISO) data-based dynamic Loewner state space model. Second, an SVD-based truncation is used on the Loewner state space model, such that the minimal, dynamically representative, state space model is achieved. For this second part, varying levels of reduction are generated and compared. The work herein can be extended to model generation using experimental measurements by replacing the FEM output data in the first step and following the same procedure. This method will be demonstrated on two thermally morphing structures, a rigidly fixed hexapod in multiple geometric configurations and a low mass anisotropic morphing boom. This paper is working to detail the method and identify the benefits of the reduced model methodology. [ABSTRACT FROM AUTHOR]

When biological cells divide, they divide on a given angle. It has been shown experimentally that the orientation of cell division angle for a single cell can be described by a probability density function. However, the way in which the probability density function underlying cell division orientation influences population or tissue scale morphogenesis is unknown. Here we show that a computational approach, with thousands of stochastic simulations modeling growth and division of a population of cells, can be used to investigate this unknown. In this paper we examine two potential forms of the probability density function: a wrapped normal distribution and a binomial distribution. Our results demonstrate that for the wrapped normal distribution the standard deviation of the division angle, potentially interpreted as biological noise, controls the degree of tissue scale anisotropy. For the binomial distribution, we demonstrate a mechanism by which direction and degree of tissue scale anisotropy can be tuned via the probability of each division angle. We anticipate that the method presented in this paper and the results of these simulations will be a starting point for further investigation of this topic. [ABSTRACT FROM AUTHOR]

In a previous paper, Duchêne and Rigo introduced the notion of invariance for take-away games on heaps. Roughly speaking, these are games whose rulesets do not depend on the position. Given a sequence S of positive tuples of integers, the question of whether there exists an invariant game having S as set of P -positions is relevant. In particular, it was recently proved by Larsson et al. that if S is a pair of complementary Beatty sequences, then the answer to this question is always positive. In this paper, we show that for a fairly large set of sequences (expressed by infinite words), the answer to this question is decidable. [ABSTRACT FROM AUTHOR]

In this paper, a new 4H-SiC trench-gate IGBT structure incorporated a P + shielding region in the emitter side is proposed in order to reduce the on-state voltage drop. Through the 2-D ATLAS simulation, the characteristics of the proposed structure are investigated and compared with the conventional structure. The simulation results indicate that the proposed structure exhibits an improvement in the following. Firstly, the on-state voltage drop is reduced by 32.75%. Secondly, the differential specific on-resistance is reduced by 42.33%. Finally, under the same on-state voltage drop, the turn-off energy is reduced more than 50.00%. At the end of the paper, it is explored that what effects the physical parameter of the P + shielding region in the proposed structure have on the steady state performances. [ABSTRACT FROM AUTHOR]

The paper provides a comparative investigation on accuracy and conservation properties of two particle regularization schemes, namely, the Dynamic Stabilization (DS) [1] and generalized Particle Shifting (PS) [2] schemes in simulations of both internal and free-surface flows in ISPH (Incompressible SPH) context. The paper also presents an Optimized PS (OPS) scheme for accurate and consistent implementation of particle shifting for free-surface flows. In contrast to PS, the OPS does not contain any tuning parameters for free-surface, consistently resulting in perfect elimination of shifting normal to an interface and resolves the unphysical discontinuity beneath the interface, seen in PS results. [ABSTRACT FROM AUTHOR]

Distributed Dynamic Thermal Management (DDTM) schemes are widely being used nowadays to cater for the elevated chip temperatures for many-core systems. Traditionally, DDTM schemes are analyzed using simulation or emulation but the non-exhaustive and incomplete nature of these analysis techniques may compromise on the reliability of the chip. Recently, model checking has been proposed for formally verifying simple DDTM schemes but, despite several abstractions, the analysis is limited to less than 100 cores due to the state-space explosion problem. As a more scalable approach for next-generation many-core systems, we propose a methodology based on theorem proving to perform formal verification of DDTM schemes. The proposed approach allows specification and verification of both functional and timing properties for any number of cores and for all times. For this purpose, the paper provides a higher-order-logic formalization of a generic DDTM scheme. The proposed generic model can be specialized to formally specify most of the existing DDTM schemes and thus formally verify their thermal properties, like temperature bounds and balancing and time to reach thermal stability, as higher-order-logic theorems. As an illustrative example, the paper presents a formal model and analysis of a Distributed Task Migration based DDTM scheme for many-core systems. [ABSTRACT FROM AUTHOR]

This paper aims at investigating the buckling load of fully deployed linear array deployable structure based on scissor-like element (SLE) under its own weight. The deployable structure has been widely researched both in geometric configurations and structural dynamic characteristics. However, when the number of elements or degree of deployment exceeds the predetermined range, even if there is no external load, deployable structure will automatically collapse under its own weight. To address this issue, this paper derives a new stability model based on linear elastic analysis and energy method to compute the buckling load caused by its own weight for avoiding the structural instability, which can be applied to a linear array deployable structure with n SLEs. In the process of calculation, the first SLE is taken for mechanical analysis and the results are extended to any unit. In the sequel of this process, the scissor deployable structure is equivalent to a uniform solid column and its buckling condition under self-weight is obtained based on the principle of potential energy. Also, the effect of various parameters that affect the instability of the structure, such as the number of elements, bar length and degree of deployment is investigated, and the results of the theoretical analysis are verified through a comparison with the simulation results in ANSYS, which show that the new stability model proposed here can predict the buckling load of scissor deployable structure. [ABSTRACT FROM AUTHOR]

Fispact-II is a code system and library database for modelling activation-transmutation processes, depletion-burn-up, time dependent inventory and radiation damage source terms caused by nuclear reactions and decays. The Fispact-II code, written in object-style Fortran, follows the evolution of material irradiated by neutrons, alphas, gammas, protons, or deuterons, and provides a wide range of derived radiological output quantities to satisfy most needs for nuclear applications. It can be used with any ENDF-compliant group library data for nuclear reactions, particle-induced and spontaneous fission yields, and radioactive decay (including but not limited to TENDL-2015, ENDF/B-VII.1, JEFF-3.2, JENDL-4.0u, CENDL-3.1 processed into fine-group-structure files, GEFY-5.2 and UKDD-16), as well as resolved and unresolved resonance range probability tables for self-shielding corrections and updated radiological hazard indices. The code has many novel features including: extension of the energy range up to 1 GeV; additional neutron physics including self-shielding effects, temperature dependence, thin and thick target yields; pathway analysis; and sensitivity and uncertainty quantification and propagation using full covariance data. The latest ENDF libraries such as TENDL encompass thousands of target isotopes. Nuclear data libraries for Fispact-II are prepared from these using processing codes PREPRO, NJOY and CALENDF. These data include resonance parameters, cross sections with covariances, probability tables in the resonance ranges, PKA spectra, kerma, dpa, gas and radionuclide production and energy-dependent fission yields, supplemented with all 27 decay types. All such data for the five most important incident particles are provided in evaluated data tables. The Fispact-II simulation software is described in detail in this paper, together with the nuclear data libraries. The Fispact-II system also includes several utility programs for code-use optimisation, visualisation and production of secondary radiological quantities. Included in the paper are summaries of results from the suite of verification and validation reports available with the code. [ABSTRACT FROM AUTHOR]

The interference pattern of the sound field of a broadband source in a shallow water waveguide is studied theoretically and experimentally in this paper. In the ocean waveguide, the sound source generates the interference pattern of the intensity distribution (interferogram) in the frequency–time domain. The mathematical theory of the interferogram structure is developed. The source interferogram consists of a set of quasi-parallel interference fringes in the frequency–time domain. It is shown that the slope of the interference fringes depends on the distance, velocity, and direction of motion of the sound source. The relationship between the slope angle of the interference fringes in the interferogram and the source parameters is derived in the paper. The two-dimensional Fourier transform (2D-FT) is used to analyze the interferogram. The result of the 2D-FT is called the Fourier hologram (hologram). It is shown that the hologram consists of a few focal spots in a relatively small area. The presence of these focal spots is the result of the interference of acoustic modes with different wavenumbers. The mathematical theory of the hologram structure is developed in this paper. The relationship between the coordinates of the focal spots on the hologram and the source parameters is considered. Consequently, the position of the focal spots can be used to estimate the source parameters (range, velocity, and direction of motion). The theoretical conclusions are verified in the context of computer modeling and the results of the acoustic experiment on the Pacific shelf (Yellow Sea, April, 2004) in the band 180–220 Hz. • Moving source interferogram consists of a set of parallels in frequency–time domain. • Relationship between the fringes slope angle and the source parameters. • Hologram (2D-FT of interferogram) consists of a few focal spots in a small area. • Derivation of relationship between the spots coordinates and the source parameters. • Verification of theoretical results by computer modeling and in real experiments. [ABSTRACT FROM AUTHOR]

Missing data occur frequently in a wide range of applications. In this paper, we consider estimation of high-dimensional covariance matrices in the presence of missing observations under a general missing completely at random model in the sense that the missingness is not dependent on the values of the data. Based on incomplete data, estimators for bandable and sparse covariance matrices are proposed and their theoretical and numerical properties are investigated. Minimax rates of convergence are established under the spectral norm loss and the proposed estimators are shown to be rate-optimal under mild regularity conditions. Simulation studies demonstrate that the estimators perform well numerically. The methods are also illustrated through an application to data from four ovarian cancer studies. The key technical tools developed in this paper are of independent interest and potentially useful for a range of related problems in high-dimensional statistical inference with missing data. [ABSTRACT FROM AUTHOR]