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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 concerned with the dynamical stability of spiky steady states to a chemotaxis-consumption model with signal-dependent motilities on the half space, where no-flux boundary condition for the bacteria and inhomogeneous Dirichlet boundary condition for the nutrient are prescribed. The motilities of bacteria depend on the concentration of nutrient in the form of power law, which means that they are degenerate if the power-law exponent is positive and are singular if the exponent is negative at the zero state of nutrient. We show that in both cases the spiky patterns admitted by the model are nonlinearly stable under appropriate perturbations. We introduce a unified approach to dealing with both degeneracy and singularity in the diffusivity for this model. The approach is based on a combination of weighted energy estimates and weighted elliptic estimates, where various weights are artfully constructed to capture the complex behaviors of solutions near the zero state. Numerical simulations are also carried out to confirm our 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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

In this paper, we study an impulsive reaction-advection-diffusion model given by a reaction-advection-diffusion equation with the Allee effect in high-dimensional space composed with a discrete-time map. We establish the existence, uniqueness up to translation, and global stability of bistable traveling waves for impulsive reaction-advection-diffusion models. The methods involve the monotone semiflow approach, the upper and lower solutions, and spreading speeds of monostable systems. Numerical simulations verify the correctness of our conclusions. [ABSTRACT FROM AUTHOR]

This paper provides the first Liapunov coefficient formula of 3D Lotka-Volterra equations. This formula gives applications to stability of positive equilibrium and to detecting sub/super criticality of Hopf bifurcation. For 3D competitive Lotka-Volterra equations, combining this formula with the Poincaré-Bendixson theorem, we obtain criteria on multiplicity of limit cycles among Zeeman's classes 27-31, and present a series of examples to admit at least two limit cycles, which are rigorously proved by the first Liapunov coefficient formula, rather than by symbolic computation using Maple. A new Hopf bifurcation that all 2 × 2 principal minors of the community matrix are positive is found, and numerical simulation reveals its global limit cycle bifurcations are plenty. [ABSTRACT FROM AUTHOR]

In this paper, we study a three-stage tick population model with three development delays. Using the total delay τ as the bifurcation parameter, we conduct local and global Hopf bifurcation analysis. Especially, we examine the onset and termination of Hopf bifurcations of periodic solutions from the unique positive equilibrium. We locate all of the stability switches for the equilibrium and demonstrate that the global Hopf bifurcation branches are bounded. This result implies the system undergoes oscillatory behavior only with bounded delays. The key step in the proof is the exclusion of 2 τ -periodic solutions due to the negative Lozinskiĭ measure of the corresponding compound matrix. Numerical simulations are provided to show the complicated patterns of the tick population when the development delays are altered by the temperature and other environmental factors. [ABSTRACT FROM AUTHOR]

Shock electrodialysis (shock ED), an emerging nonlinear electrokinetic process for water treatment, has recently showed its capability to selectively remove multivalent cations from electrolyte mixtures. However, the mechanisms have not been understood yet. Based on the depth-averaged model developed in the first-part of the series paper for planer shock ED system, this work focuses on the mechanisms of selective ion removal. We first assume plug feed flow and do scaling analysis, and identify three possible mechanisms of selective removal of multivalent cations: smaller concentration left behind deionization zone, affinity to the charged surface where non-slip boundary slows down the velocity, and stronger push-back by streaming potential. Then we use numerical simulations to prove our hypothesis and show additional contribution from electroosmotic flow. Simulation results show that Mg is more removed from Na-Mg-Cl mixture at overlimiting current, which is qualitatively consistent with experiment results in literature. [ABSTRACT FROM AUTHOR]

This work addresses the problem of numerical simulation of the dynamic loads generated during a dry dam break flow impact on a wall. The numerical model used is the multi-fluid Navier–Stokes Volume Of Fluid (VOF) model THETIS. The results are compared with two experiments allowing pressure evolution validation at two relative positions on the wall. A first analysis of the results shows the large spatial and temporal variability of the pressure field after impact, highlighting the need for extreme care when performing measurements. When using first a free-slip boundary conditions on the bottom, the computed pressure peaks are found to behave differently depending on the distance to the stagnation point. Above a certain position, which is determined in the paper, computed peak pressures are stable with resolution while under this position, a divergent behavior is observed. This divergence is attributed to the shape of the bore tip which is poorly resolved with our model when a free-slip condition is used. This is confirmed by showing that starting from an identical free surface profile right before impact, the pressure peaks are convergent. The pressure peak instability problem can be solved by resolving the boundary layer structure with a suitable model (in our paper a v 2 − f RANS model) but this requires much more CPU resources. [ABSTRACT FROM AUTHOR]

One of the fundamental tasks in the development of wireless sensor networks is coverage, which measures the network effectiveness and accuracy in event detection. While most existing studies on coverage focus on homogeneous and static wireless sensor networks, where the sensors have the same features, such as sensing, communication, and initial energy reserve, this paper considers heterogeneous sensors and sink mobility, which provide a more realistic and accurate view of the network design for a variety of sensing applications. In this paper, we exploit Helly’s Theorem to address the joint problem of k -coverage and data collection in heterogeneous wireless sensor networks, where each point in a field of interest is simultaneously covered by at least k active heterogeneous sensors. More precisely, we introduce a global framework that jointly considers k -coverage and data collection. Precisely, we propose a multi-tier (or hierarchical) architecture of heterogeneous sensors along with two data collection protocols. While the first protocol is based on an adaptive hybrid forwarding scheme, the second one uses a mobile sink to collect the sensed data from all the sensors in the network. To this end, we investigate the optimal mobility strategy of the sink in order to minimize the average total energy consumption due to both of data communication and sink mobility in a circular sensor field. We divide the field into concentric circular bands with the same width, and derive a closed-form solution for the optimal sink mobility. We corroborate our analysis with simulation results to assess our proposed framework. We find that our sink mobility-based data collection protocol outperforms our hybrid geographic forwarding-based data collection protocol. [ABSTRACT FROM AUTHOR]

Sense-making plays an important role in Intelligence Analysis, but can be difficult to study in situ. Thus, it is useful to exploit training exercises to study this phenomenon. In this paper two versions of the same exercise are reported: one undertaken by participants at a conference and one undertaken by Military Intelligence personnel. The behaviour of groups of analysts (experienced versus inexperienced) is considered in terms the Data/Frame model of sense-making. The paper illustrates how Intelligence Analysis often involves parallel and overlapping explorations of data, with multiple frames that might be minimal and sketchy. The use of representations, such as link diagrams, provides a means of externalising frames and it is suggested that these can shift the style of reasoning exhibited by the teams as the Exercise progresses. Such a shift was seen more clearly in the behaviour of the Military Intelligence Officers who also spent more time developing and refining the diagrams to support the presentation of their findings. [ABSTRACT FROM AUTHOR]

In this paper, we study the minimal speed (spreading speed) selection mechanism of traveling waves to a periodic diffusive Lotka-Volterra model with monostable nonlinearity. The method of upper and lower solutions pair is applied to establish the existence of traveling waves. We prove that the nature of nonlinear selection is to find a lower solution pair with the first species decaying in a faster rate. By novel constructions of various upper and lower solutions, we obtain a number of new results on the minimal speed determinacy. Numerical simulations are carried out to illustrate all of our discoveries. [ABSTRACT FROM AUTHOR]

In this paper, the dynamics of a general predator-prey system with diffusion and stage structures are investigated. Under some assumptions, the stability of positive steady state and the existence of local Hopf bifurcation are obtained by analyzing the distribution of eigenvalues. Moreover, the global existence of positive periodic solution is established by using the global Hopf bifurcation result of Wu. Finally, an example and some numerical simulations are carried out for illustrating the theoretical results. [ABSTRACT FROM AUTHOR]

Recent numerical simulations have shown the existence of multiple self-similar solutions to the Cauchy problem for the 2-dimensional incompressible Euler equation, with initial vorticity in L l o c p (R 2) , 1 ≤ p < + ∞. Toward a rigorous validation of these computations, in this paper we analytically construct self-similar solutions (i) on an outer domain of the form { | x | > R } , and (ii) in a neighborhood of the points where the solution exhibits a spiraling vortex singularity. The outer solution is obtained as the fixed point of a contractive transformation, based on the Biot-Savart formula and integration along characteristics. The inner solution is constructed using a system of adapted coordinates, following the approach of V. Elling (2016) [17]. [ABSTRACT FROM AUTHOR]

The prevalent description of low capillary number two-phase flow in porous media relies on the independence of phase transport. An extended Darcy’s law with a saturation dependent effective permeability is used for each phase. The driving force for each phase is given by its pressure gradient and the body force. This diagonally dominant form neglects momentum transfer from one phase to the other. Numerical and analytical modeling in regular geometries have however shown that while this approximation is simple and acceptable in some cases, many practical problems require inclusion of momentum transfer across the interface. Its inclusion leads to a generalized form of extended Darcy’s law in which both the diagonal relative permeabilities and the off-diagonal terms depend not only on saturation but also on the viscosity ratio. Analogous to application of thermodynamics to dynamical systems, any of the extended forms of Darcy’s law assumes quasi-static interfaces of fluids for describing displacement problems. Despite the importance of the permeability coefficients in oil recovery, soil moisture transport, contaminant removal, etc., direct measurements to infer the magnitude of the off-diagonal coefficients have been lacking. The published data based on cocurrent and countercurrent displacement experiments are necessarily indirect. In this paper, we propose a null experiment to measure the off-diagonal term directly. For a given non-wetting phase pressure-gradient, the null method is based on measuring a counter pressure drop in the wetting phase required to maintain a zero flux. The ratio of the off-diagonal coefficient to the wetting phase diagonal coefficient (relative permeability) may then be determined. The apparatus is described in detail, along with the results obtained. We demonstrate the validity of the experimental results and conclude the paper by comparing experimental data to numerical simulation. [ABSTRACT FROM AUTHOR]

The paper presents the results of experimental studies of vibrations of an elastic hose which are induced by a pulsating fluid flow. It was found that there is a possibility of parametric resonances: principal and combination associated with certain modes of vibrations. The influence of frequency and the amplitude of pulsation, average flow velocity, pressure inside pipe, the length of the hose, and the temperature on the ranges of parametric vibrations were analysed. The character of vibrations in resonance ranges was determined by showing time histories and the results of spectral analyses. A flexible hose applied in high-pressure hydraulic systems was used as an object of research. The values of basic parameters which describe the hose׳s mechanical properties were identified experimentally. The results of the experiments were compared with the results of numerical simulations conducted on the basis of the methodology proposed in Part I of this paper. [ABSTRACT FROM AUTHOR]

This paper is devoted to the analytical study of initial–boundary value problems for a system of hyperbolic balance laws derived from a repulsive chemotaxis model with logarithmic sensitivity. In the first part of the paper we show that, subject to the Dirichlet boundary conditions, classical solutions exist globally in time for large initial data. Asymptotically in time, the solutions are shown to converge to their boundary data at an exponential rate as time goes to infinity. Numerical simulations are supplied to corroborate the analytical results. The analytic approach developed herein can be utilized to handle a family of initial and initial–boundary value problems of the model and related models with similar mathematical structure. As a demonstration of the effectiveness of our approach, in the second part of the paper we show that, subject to the Neumann–Dirichlet boundary conditions, classical solutions exist and converge to constant equilibrium states for large initial data and for arbitrary values of the chemical diffusion coefficient. This improves a previous result obtained in [30] where the smallness of the chemical diffusion coefficient was required. [ABSTRACT FROM AUTHOR]

In this paper, the second in a series, the authors have extended and implemented their computational algorithms for improving the scalability of CSD (Computational Structural Dynamics) and FSI (Fluid-Structure Interaction) simulations on emerging architectures like multicore High Performance Computing (HPC) platforms. These algorithmic developments and extensions are classified into two categories: (i) enhanced scalability for CSD simulations on multicore platforms, (ii) newer ideas for running FSI simulations. In the first category, the authors employed the ideas developed in the first paper of this series including the multilevel partitioning strategy, next generation optimized communication procedure and better memory management to get enhanced scalability for CSD simulations. In the second category, the authors came up with a novel solver specific multicore-FSI optimal partitioning so as to improve the overall FSI scalability. After implementing the new "intelligent partitioning" algorithm, a speedup ratio of nearly 2.5x was obtained for the total time. The intelligent partitioning algorithm optimizes the number of solid domains relative to the number of fluid domains to optimize the overall FSI solution, irrespective of the type of the flow solver. In general, the authors have demonstrated (i) good, almost linear scalability for aeroelastic applications with several millions of cells on multicore platforms with thousands of cores, (ii) significant improvement in the scalability for smaller FSI problems using the intelligent partitioning. [ABSTRACT FROM AUTHOR]

In this paper, we propose and investigate a stochastic algal growth model with the explicit incorporation of season-dependent light and nutrient availability. We first establish the threshold 〈 λ 〉 ϖ that determines the persistence and extinction of the algae: when 〈 λ 〉 ϖ > 0 , the algal will persist in mean, while when 〈 λ 〉 ϖ < 0 , the algae will eventually die out. Then we prove the existence and global attractiveness of a positive stochastic periodic solution when 〈 λ 〉 ϖ > 0 by constructing suitable Lyapunov functions. Numerical simulations are carried out to substantiate our analytical results and investigate effective methods to control algal blooms. • We propose a stochastic algal growth model incorporating explicitly seasonal light intensity and nutrient availability. • We establish the stochastic threshold 〈 λ 〉 ϖ that determines the persistence and extinction of algae. • The existence and global attractiveness of a positive stochastic periodic solution are proved. • Numerical simulations are carried out to substantiate our analytical results. [ABSTRACT FROM AUTHOR]

The global dynamics and regularity of parabolic-hyperbolic systems is an interesting topic in PDEs due to the coupling of competing dissipation and hyperbolic effects. This paper is concerned with the Cauchy problem of a parabolic-hyperbolic system derived from a chemotaxis model describing the dynamics of the initiation of tumor angiogenesis. It is shown that, as time tends to infinity, the Cauchy problem with large-amplitude discontinuous data admit global weak solutions which converge to a constant state (resp. a viscous shock wave) if the asymptotic states of initial values at far field are equal (resp. unequal). Our results improve the previous results where initial value was required to be continuous and have small amplitude. Numerical simulations are performed to verify our analytical results, illustrate the possible regularity of solutions and speculate the minimal regularity of initial data required to obtain the smooth (classical) solutions of the concerned parabolic-hyperbolic system. [ABSTRACT FROM AUTHOR]

In this paper we study speed selection for traveling wavefronts of the lattice Lotka-Volterra competition model. For the linear speed selection, by constructing new types of upper solutions to the system, we widely extend the results in the literature. We prove that, for the nonlinear speed selection, the wavefront of the first species decays with a faster rate at the far end. This enables us to construct novel lower solutions to establish the existence of pushed wavefronts, a topic that has been understudied. We raise a new conjecture related to the classical Hosono's version of the diffusive system and our numerical simulations help to confirm it, while our rigorous results only provide a partial answer. [ABSTRACT FROM AUTHOR]