Explicit Formulation Research Articles

Adaptive Learning and Sampled-Control for Nonlinear Game Systems Using Dynamic Event-Triggering Strategy.

Static event-triggering-based control problems have been investigated when implementing adaptive dynamic programming algorithms. The related triggering rules are only current state-dependent without considering previous values. This motivates our improvements. This article aims to provide an explicit formulation for dynamic event-triggering that guarantees asymptotic stability of the event-sampled nonzero-sum differential game system and desirable approximation of critic neural networks. This article first deduces the static triggering rule by processing the coupling terms of Hamilton-Jacobi equations, and then, Zeno-free behavior is realized by devising an exponential term. Subsequently, a novel dynamic-triggering rule is devised into the adaptive learning stage by defining a dynamic variable, which is mathematically characterized by a first-order filter. Moreover, mathematical proofs illustrate the system stability and the weight convergence. Theoretical analysis reveals the characteristics of dynamic rule and its relations with the static rules. Finally, a numerical example is presented to substantiate the established claims. The comparative simulation results confirm that both static and dynamic strategies can reduce the communication that arises in the control loops, while the latter undertakes less communication burden due to fewer triggered events.

Micromechanical approach to effective viscoelastic behavior of jointed rocks

Assessing the overall instantaneous behavior and strength properties of jointed materials have been the subject of important investigations in the last decades, including phenomenological or micromechanics-based contributions. However, less attention has been dedicated to delayed component of deformation in such media. This issue is addressed in this paper, which is devoted to the formulation of a micromechanical approach to effective viscoelastic properties of jointed rocks with consideration of constituents aging. At the scale of representative elementary volume (REV), the joints are modeled as planar interfaces whose behavior is described by means of generalized viscoelastic state equations under normal and shear loading conditions. Closed-form expressions for the homogenized creep tensor are derived from solving an appropriate viscoelastic concentration problem stated on the REV. The local strain and displacement jump fields are analyzed by extending the concept of strain concentration to relate the components of joint displacement jump to macroscopic strain. Main features of the theoretical overall creep behavior, such as the anisotropy associated with the privileged joint orientations, are highlighted through explicit formulations in some particular configurations of the jointed medium. Finally, the ability of the approach to accurately reproduce the creep behavior of jointed media is assessed by comparison with experimental data as well as with finite element solutions derived in the context of multilayered stratified composite modeling.

Effects of a self-regulating writing course on academic text production in a PhD and Master sample

Objective: This article presents the results of a study with an experimental design; whose objective was to examine the effects of a virtual learning environment focused on the self-regulation of writing on the development of self-regulation and academic writing skills. Background: The course design presented here is based on the idea that writing should be taught as a process, not as a product, which requires training students in the use of cognitive and metacognitive strategies. For this reason, the course set out to increase two skills: 1) the ability to self-regulate academic text writing process and 2) metacognitive awareness. Methodology: In an experimental design, 46 master and doctoral students participated in the 12 – week course, designed to be implemented in an online modality, through the Moodle learning management system. Given the self-regulating nature of this intervention proposal, didactic tools were created enabling the subject to identify and learn about their own processes and the resources they usually employ to develop writing tasks. To that end, the course has two specific strategies: a self-regulating writing scaffolding (SWS) and different tools to increase metacognitive awareness (IMA). The effects of these strategies were observed separately and combined. Results: A first aspect to consider with respect to the effects of the SWS on factors associated with self-regulation is the increase in motivation at the end of the intervention, this, by incorporating strategies such as the explicit formulation of goals, self-evaluation and the explanation of the usefulness and functionality of the task. Regarding achievements reached in improving writing, the SWS also proves to be the most effective for this purpose. Modelling specific behaviours such as choosing specific objectives for the writing task, the formulation of a defined and explicit plan, monitoring behaviours, self-evaluation and self-reinforcement are determinants to reach higher levels of writing.

Effect of rotational inertia on building response to earthquakes via a closed-form solution

In this article, a widely used building model, comprised of uniform coupled flexural and shear beams, herein improved by allowing for the effects of rotational inertia. Closed-form solutions in terms of trigonometric and hyperbolic functions are obtained, allowing for the explicit formulation of period ratios, modal participation factors (MPFs), mode shapes, and mode shape derivatives based solely on displacement response, without coupling with chord rotations, which is the case for the Timoshenko beam model. This makes the model proposed in this study more convenient for assessing building behavior to ground motion, by explicitly highlighting the effect of rotational inertia in their response to earthquakes, making the case for studying its beneficial effects in mitigating response of buildings to ground motion. It is observed that rotational inertia induces mild fundamental period lengthening, while notably reducing period ratios between higher modes and the fundamental one. This can lead to an enhanced response to ground motion showcasing narrow-band characteristics. However, the most severe effect is found to be on the MPF, which is significantly diminished. This leads to important reductions on the overall response, as a consequence of attenuation of the first-mode response, along with severe undercutting of the effects of higher modes. The results demonstrate that without considering the rotational inertia in the assessment of in-plane structural response to horizontal ground motion can lead to conservative results. Moreover, the results showcase the advantages of providing supplemental rotational inertia as a way to improve the seismic behavior of buildings.

The azimuthal dependence of Rayleigh wave ellipticity in a slightly anisotropic medium

SUMMARYA recent study analysed the Rayleigh wave ellipticity obtained by ambient noise cross-correlation in periods of 8–20 s, and observed the Rayleigh wave ellipticity is backazimuth-dependent with a 180° periodicity in the contiguous United States. However, the azimuthal anisotropic parameters have not been inverted to depths, and the comparison with other seismic results has not been possible so far, partially due to the lack of related theoretical investigations. Here, we first derive explicit formulation to relate the period-dependent backazimuthal Rayleigh wave ellipticity with the depth-dependent azimuthal wave speed variation in a slightly anisotropic medium based on the variational principle; by carefully examining relations among different parametrizations of a horizontally transverse isotropic medium, we then express the final formulation in terms of Crampin’s notation. The formulation is verified by comparison with the results of anisotropic propagator matrix technique. Tests show the backazimuth-dependent Rayleigh wave ellipticity provides complementary information on anisotropic parameters in addition to the widely used phase velocity. A simple application of the derived formulation to real data in North America is also provided. Our formulation can be regarded as an extension of the classic work on azimuthal-dependent phase velocity, and helps to quantitatively explain the backazimuth-dependent Rayleigh wave ellipticity.

Three-dimensional hybrid asynchronous perfectly matched layer for wave propagation in heterogeneous semi-infinite media

This paper presents an efficient hybrid asynchronous three-dimensional (3D) perfectly matched layer (PML) for modeling unbounded domains. The proposed unsplit explicit or implicit 3D PML formulation is implemented in the framework of a heterogeneous asynchronous time integrator. It is fully versatile in terms of time integrators and time step sizes according to partitions while conserving classical finite element formulations in the elastic domain without complex-valued stretched coordinates. Examples of a semi-infinite bar, Lamb’s test, and a soil–structure interaction problem with PML-truncated semi-infinite heterogeneous media are investigated to illustrate the efficiency of the proposed PML in terms of accuracy and CPU time.

Simple approach for including foundation–soil–foundation interaction in the static stiffnesses of multi-element shallow foundations

In common engineering practice, foundation–soil–foundation interaction of shallow foundations is frequently ignored. This is presumably for cost/benefit reasons, since computationally demanding finite-element and/or boundary element models are required for that purpose, and its effects are usually assumed to be negligible. In this sense, the present paper provides a simple and inexpensive way of incorporating foundation–soil–foundation interaction through a numerically explicit stiffness matrix formulation. The necessary ingredients for homogeneous and non-homogeneous (shear modulus power-law variation with depth) half-spaces are given. The proposed approach is then applied to offshore wind turbines’ multiple suction caisson foundations (tripod and tetrapod), where it is observed that the foundation–soil–foundation interaction is significant. Its range of validity is also established, and valuable ready-to-use closed-form formulas for the correction factors of the stiffnesses of tripod and tetrapod groups are also derived. The methodology is applicable as long as the spacing between foundations is somewhat greater than the foundation depth.

Ultimate axial capacity prediction of CCFST columns using hybrid intelligence models - a new approach

This study aims to propose a new intelligence technique of predicting the ultimate capacity of axially loaded circular concrete-filled steel tube (CCFST) columns. A hybrid system based on one of the evolution algorithm – Genetic Algorithm (GA), fused with a well-known data-driven model of multivariate adaptive regression splines (MARS), namely G-MARS, was proposed and applied. To construct the MARS model, a database of 504 experimental cases was collected from the available literature. The GA was utilized to determine an optimal set of MARS's hyperparameters, to improve the prediction accuracy. The compiled database covered five input variables, including the diameter of the circular cross section-section (D), the wall thickness of the steel tube (t), the length of the column (L), the compressive strength of the concrete (fc), and the yield strength of the steel tube (fy). A new explicit formulation was derived from MARS in further analysis, and its estimation accuracy was validated against a benchmark model, G-ANN, an artificial neural network (ANN) optimized using the same metaheuristic algorithm. The simulation results in terms of error range and statistical indices indicated that the derived formula had a superior capability in predicting the ultimate capacity of CCFST columns, relative to the G-ANN model and the other existing empirical methods.

Deep Magnification-Flexible Upsampling Over 3D Point Clouds.

This paper addresses the problem of generating dense point clouds from given sparse point clouds to model the underlying geometric structures of objects/scenes. To tackle this challenging issue, we propose a novel end-to-end learning-based framework. Specifically, by taking advantage of the linear approximation theorem, we first formulate the problem explicitly, which boils down to determining the interpolation weights and high-order approximation errors. Then, we design a lightweight neural network to adaptively learn unified and sorted interpolation weights as well as the high-order refinements, by analyzing the local geometry of the input point cloud. The proposed method can be interpreted by the explicit formulation, and thus is more memory-efficient than existing ones. In sharp contrast to the existing methods that work only for a pre-defined and fixed upsampling factor, the proposed framework only requires a single neural network with one-time training to handle various upsampling factors within a typical range, which is highly desired in real-world applications. In addition, we propose a simple yet effective training strategy to drive such a flexible ability. In addition, our method can handle non-uniformly distributed and noisy data well. Extensive experiments on both synthetic and real-world data demonstrate the superiority of the proposed method over state-of-the-art methods both quantitatively and qualitatively. The code will be publicly available at https://github.com/ninaqy/Flexible-PU.

Solução de um Problema de Transporte de Contaminante em Corpos Hídricos Utilizando o Método dos Volumes Finitos

As water is one of the fundamental resources for the quality of life and existence of future generations, environmental preservation becomes the duty of every human being. However, the existence of some type of pollution in most rivers in Brazil is noteworthy and, faced with situations like this worldwide, the United Nations itself emphasizes the importance of having an excellent control over the quality of these water bodies. Thus, the present work sought to simulate a scenario of accidental pollution in the watercourse, in order to formulate and implement a mathematical model, in which its numerical result approaches the real problem about the transport of contaminants in rivers, with data experimental results obtained in fieldwork carried out on the São Pedro River, which is located in the mountainous region of the State of Rio de Janeiro. For the modeling, we used a one-dimensional mathematical model solved using the Finite Volume Method, with the explicit and implicit formulations, which are based on multiple integrals and Taylor series. The numerical results were observed to be close to the real problem related to the transport of contaminants in rivers.

Dual representation of expectile-based expected shortfall and its properties

<p style='text-indent:20px;'>An expectile can be considered a generalization of a quantile. While expected shortfall is a quantile-based risk measure, we study its counterpart—the expectile-based expected shortfall—where expectile takes the place of a quantile. We provide its dual representation in terms of a Bochner integral. Among other properties, we show that it is bounded from below in terms of the convex combination of expected shortfalls, and also from above by the smallest law invariant, coherent, and comonotonic risk measures, for which we give the explicit formulation of the corresponding distortion function. As a benchmark to the industry standard expected shortfall, we further provide its comparative asymptotic behavior in terms of extreme value distributions. Based on these results, we finally explicitly compute the expectile-based expected shortfall for selected classes of distributions.</p>

A Conforming A-FEM for Modeling Arbitrary Crack Propagation and Branching in Solids

In this paper, an improved conforming AFEM (C-AFEM) for efficient modeling of arbitrary crack propagation and branching is proposed and validated. An explicit formulation for branching cracks has been derived within the C-AFEM framework. The conjugate gradient method is integrated into the C-AFEM formulation to solve the local problem that consists of all elements traversed by single or multiple cracks. Multiple numerical evidences show that this new approach can substantially improve the modeling efficiency. The solution accuracy and numerical robustness are also significantly improved.

Pati-Salam Model in Curved Space-Time from Square Root Lorentz Manifold

There is a ( ) ( ) 4' 4 UU × -bundle on four-dimensional square root Lorentz manifold. Then a Pati-Salam model in curved space-time (Lagrangian) and a gravity theory (Lagrangian) are constructed on square root Lorentz manifold based on self-parallel transportation principle. An explicit formulation of Sheaf quantization on this square root Lorentz manifold is shown. Sheaf quantization is based on superposition principle and construct a linear Sheaf space in curved space-time. The transition amplitude in path integral quantization is given which is consistent with Sheaf quantization. All particles and fields in Standard Model (SM) of particle physics and Einstein gravity are found in square root metric and the connections of bundle. The interactions between particles/fields are described by Lagrangian explicitly. There are few new physics in this model. The gravity theory is Einstein-Cartan kind with torsion. There are new particles, right handed neutrinos, dark photon, Fiona, c X ± and 01212 ** ,, ,, Y YY YY

Axisymmetric Electromagnetic Wave Propagation Computation Using the Constrained Interpolation Profile Scheme With Large Time Steps

Conventional explicit time-domain methods used to solve Maxwell's equations are reliable and robust but are conditionally stable and often require the fulfillment of the condition Courant-Friedrichs-Lewy (CFL) ≤ 1. While this is acceptable for many applications, in some instances, where Maxwell's equations are solved alongside systems with slower propagation velocities, explicit methods prove costly. This is the case for nonrelativistic electromagnetic Particle-In-Cell methods that are required to study plasma thrusters. Several algorithms have been proposed to retain a nearly explicit formulation using large time steps to achieve higher CFL values. Among these is the semi-Lagrangian constrained interpolation profile (CIP) method. While the ability of this method to handle CFL > 1 has been demonstrated for planar 2-D-3-D cases, this has not been done for 2-D cases with cylindrical symmetry. In this article, a procedure is presented to compute the electromagnetic wave propagation in 2-D domains with cylindrical symmetry using the CIP method. The CIP scheme is extended for CFL ≥ 1 cases, and a ghost node method is proposed to deal with the axis singularity and with the wall boundary condition. The results are compared with the fields of a Hertzian dipole and with a coaxial cable, and they show a good agreement.

Multinational Corporations and Local Content Policy: Towards a New Equilibrium

Multinational corporations operate beyond state borders and the need to regulate them has been made apparent by documented human rights violations, as well as environmental encroachments. This article considers two types of measures: (1) those that have been adopted by multinational corporations themselves such as Corporate Social Responsibility initiatives and (2) those developed by host states with a focus on Local Content policy measures. Going beyond the idea of regulating corporations, Local Content policy measures are designed to act as a growth multiplier by developing linkages and involving local populations in the production process to create a spillover effect on the local or national economy. The author reviews the advantages and risks, associated with crafting such policies, and argues that demand for such measures is on the rise, not just in high value-added industries but also in other spheres. Indeed, while Local Content policies may present some disadvantages, restricting foreign contributions to the production process in an attempt to cultivate local economic linkages, their explicit formulation offers a high degree of clarity to international investors, which could facilitate and regularize the activities of multinational corporations.

An enhanced explicit time-marching procedure to analyse acoustic–elastodynamic coupled models

This paper proposes an effective approach to analyse wave propagation through coupled fluid–structure models considering explicit time-marching formulations. In this context, different explicit time-domain algorithms are applied to analyse the acoustic and elastodynamic subdomains of the model, allowing greater time-step values to be considered for the coupled analysis, improving the performance of the explicit solution. Since explicit algorithms are considered, separated analyses of the acoustic and elastodynamic subdomains may be easily carried out, with the interaction between the different subdomains of the model being accomplished by interface forces. In this work, these interface forces are computed considering an implicit formulation, allowing the stability limits of the explicit solution to be governed by the decoupled subdomains of the model; thus, enabling greater time-steps to be applied if enhanced time-marching procedures are considered within the solid subdomains (which are usually the most restrictive subdomains of the coupled model). The proposed methodology provides adaptive algorithmic dissipation in the higher modes and it is highly accurate, as well as it is very simple to implement. Numerical results are presented at the end of the manuscript, illustrating the performance and effectiveness of the new approach.

Influence of bird mass and impact height on the fan-blade of an aero-engine

The impact of birds on aircraft during flight is a significant threat to passenger safety and the components of aircraft. Windshields and engine blading are vulnerable to damage. Airworthiness standards requirement states that critical structural parts should be able to withstand bird strikes to a certain level of damage criteria. In order to fulfill these requirements, bird impact response of aircraft components is evaluated by means of intensive experimental and numerical technique. Numerical methods help to reduce certification and development costs and have been increasingly adopted to analyze bird impact. Numerical simulation also predicts results which are not considered in experimental tests and helps in evaluating effectiveness of design modifications. Forces generated due to bird impact on an Engine fan blade are highly non-linear and extremely dynamic in nature. In this work, the forces and other transient behavior are analyzed using FEM techniques which are established upon explicit time-dependent formulation. The critical impact height of the designated Fan-blade was identified, which can also pave way for future work.

Development of an implicit contact technique for the material point method

An implicit contact algorithm for the material point method (MPM) has been developed to simulate contact. This allows recently developed implicit MPM codes to simulate large-scale deformations and interaction with external bodies. The performance of the method has been investigated and compared to an existing explicit method using benchmark and geotechnical examples. In particular, the proposed formulation has been shown to conserve energy in a similar way to the explicit formulation and reach similar results. The method typically converges to the analytical solution when an adequate time step and mesh size are used, with the time step generally being around ten times larger than the explicit method, although during the contact phase this does not always result in faster computation due to the iterative solution procedure.

The Target Trial: A Powerful Device Beyond Well-defined Interventions.

The Target Trial: A Powerful Device Beyond Well-defined Interventions.

Simultaneous Fidelity and Regularization Learning for Image Restoration.

Most existing non-blind restoration methods are based on the assumption that a precise degradation model is known. As the degradation process can only be partially known or inaccurately modeled, images may not be well restored. Rain streak removal and image deconvolution with inaccurate blur kernels are two representative examples of such tasks. For rain streak removal, although an input image can be decomposed into a scene layer and a rain streak layer, there exists no explicit formulation for modeling rain streaks and the composition with scene layer. For blind deconvolution, as estimation error of blur kernel is usually introduced, the subsequent non-blind deconvolution process does not restore the latent image well. In this paper, we propose a principled algorithm within the maximum a posterior framework to tackle image restoration with a partially known or inaccurate degradation model. Specifically, the residual caused by a partially known or inaccurate degradation model is spatially dependent and complexly distributed. With a training set of degraded and ground-truth image pairs, we parameterize and learn the fidelity term for a degradation model in a task-driven manner. Furthermore, the regularization term can also be learned along with the fidelity term, thereby forming a simultaneous fidelity and regularization learning model. Extensive experimental results demonstrate the effectiveness of the proposed model for image deconvolution with inaccurate blur kernels, deconvolution with multiple degradations and rain streak removal.