Preconditioned Method Research Articles

Features of the use of ischemic preconditioning for the correction of vibration polyneuropathy of the upper extremities

Introduction. The study of the methods for non-pharmacological correction of vibration polyneuropathy is relevant in view of the high prevalence of vibration disease in various industries, and high occurrence of disability of workers. Ischemic preconditioning has shown its effectiveness in correcting the manifestations of vibration polyneuropathies. The high frequency of nerve compression in tunnels against the background of polyneuropathic lesions in vibration disease dictates the need to study the effectiveness of the method in various forms of vibration polyneuropathy.
 The aim of the study was to investigate the effectiveness of ischemic preconditioning in various forms of vibration polyneuropathy.
 Materials and methods. Twenty nine patients with a proven diagnosis of vibration disease were examined and treated uisng the ischemic preconditioning. They were divided into 2 groups: group 1 – 18 individuals with upper extremities polyneuropathy without nerve compression, group 2 – 11 subjects with compression complications of polyneuropathy. The examinations included neurological survey, electroneuromyographic investigation before and after the course of ischemic preconditioning conducted according to a patented technique.
 Results. A decrease in sensory disturbances and improvement in the impulse conduction along the sensory fibers of the nerves of the upper extremities after a course of ischemic preconditioning in the group of the patients without compression neuropathies were noted. In the group of the patients with polyneuropathies complicated by the nerve compression in tunnels, the positive effect was less significant.
 Limitations. The study was limited by the assessment of clinical and electroneuromyographic parameters in 29 patients with vibration disease due to the exposure to local vibration before and after the course of ischemic preconditioning.
 Conclusion. The method of ischemic preconditioning is effective as a method for non-pharmacological correction of vibration polyneuropathy. Compression neuropathies are predictors of lower efficiency of the method, and therefore it is important to select patients for the treatment by this method with the preferred inclusion of the patients with uncomplicated vibration polyneuropathies.

Development of an efficient calculation technique for dynamics of mooring lines by using discrete forms of rotation

Development of efficient calculation techniques is of key importance for design of deepwater moored floating structures consisting of many subsystems, such as a floating vessel, risers and mooring lines. In particular, this study focuses on a method for simulating dynamic behavior of the mooring line, since it includes a lot of degrees of freedom and geometric nonlinear effects. A modified Morison equation based on the linear potential flow theory is employed to derive the hydrodynamic forces acting on the lines. The present approach describes the mooring lines (chain) as multi-rigid bodies based on the multibody dynamics approach. In addition, a discrete form of rotation called “the rotation update equation” is introduced. This technique approximates the rotation by using incremental components of rotation in terms of the angular velocity. This approach can bypass the parameterization of rotation in the equations of motion. Clearly, it contributes to reduction of computational costs. Furthermore, a preconditioning method is applied to the equations of motions in order to prevent the ill-conditioning which affects convergence of the numerical integration procedures for the set of equations with configuration level constraints. Finally, a comparison of results by the present method and the conventional method are presented in order to show the validity of the method.

A sine transform based preconditioned MINRES method for all-at-once systems from constant and variable-coefficient evolutionary PDEs

A sine transform based preconditioned MINRES method for all-at-once systems from constant and variable-coefficient evolutionary PDEs

Analytical Regularization Approach to Plane Wave Diffraction From Circular Hole in Infinite Resistive Plane

In this paper, the diffraction of a plane wave from a circular hole in an infinite resistive plane is addressed. In contrast to the holed perfectly electrically conducting screens, neither the equivalence principle combined with the image theory nor the Babinet principle can be applied here, and the problem has to be solved directly. The method adopted in this paper belongs to the family of the methods of analytical preconditioning. The revolution symmetry allows us to reduce the problem to an infinite set of dual integral equations in the vector Hankel transform domain for suitable unknowns vanishing outside the hole. Such equations are transformed to matrix equations by means of the Helmholtz-Galerkin discretization technique. The orthogonal eigenfunctions of the most singular part of the integral operator, reconstructing the behavior of the fields at the edge and around the center of the hole, are selected as expansion functions, thus leading to fast converging Fredholm second-kind matrix equations, whose elements can be expressed as quickly evaluable proper integrals. Numerical results show the near-field and far-field characteristics for various cases; the in-house software code is validated by means of comparisons with general-purpose commercial software.

A Hybrid Approach to Rock Pre-conditioning Using Non-explosive Demolition Agents and Hydraulic Stimulation

This study presents a novel approach to rock pre-conditioning to promote the sustainability of low-grade ore mining applications such as in-situ recovery and cave mining. The proposed method involves a two-stage hybrid approach, utilizing soundless cracking demolition agents (SCDAs) to initiate radial fractures in a predrilled host rock, followed by hydraulic stimulation to extend the fractures. SCDA injection in the first stage creates multiple radial fractures around the injection well. However, the extent of fractures is limited to the near vicinity of the injection well. To overcome this limitation, the second stage involves the application of hydraulic stimulation to extend the initiated fractures, which produces a greater fracture density compared to pure hydraulic stimulation. The concept was assessed using a fully coupled hydro-mechanical discrete element model that simulated the hybrid fracturing method on crystalline rock at the grain scale. The results indicate that the proposed method can create a high density of fractures around the injection well. Additionally, we identify and evaluate the key factors affecting the performance of the proposed method, including rock mass heterogeneity, stress anisotropy, and pre-existing defects, providing valuable insights for further experimental design and execution. Overall, the study offers promising results for a potential solution to enhance the efficiency of low-grade ore mining through the hybrid rock pre-conditioning method.

A Massively Parallel Preconditioned FEM–BEM Method for Accurate Analysis of Complex Electromagnetic Field Problems

In this letter, a parallel preconditioned FEM-BEM method is presented for the solution of challenging electromagnetic (EM) field problems, especially for calculating the radiation characteristics of electrically large radome antenna systems. A preconditioner that combining the absorbing boundary condition (ABC) with the improved additive schwarz method is first proposed for the FEM-BEM system to improve the convergence. Then, an efficient parallel framework based on message passing interface (MPI) and open multi-processing (OpenMP) is designed to achieve massively distributed parallelization of the method. Numerical results demonstrate the benefits of the proposed preconditioner over traditional additive schwarz method, as well as the accuracy and parallel scalability of the implemented method. Finally, a complex EM system consisting of a waveguide slot antenna array and a dielectric radome with more than 127 medium wavelengths is simulated to verify the capability and effectiveness of the presented method.

Ischemic preconditioning: prospects of application for the correction of physical performance in military, extreme and sports medicine

The essence of the preconditioning effect is the activation of urgent defense mechanisms of adaptation as a result of a short episode of weak, non-damaging hypoxic or ischemic exposure, which contributes to an increase in the tolerance of the subsequent delayed, more severe exposure to hypoxia or ischemia. Aim of the study was to assess the literature data on the possibility of using the method of remote ischemic preconditioning (RIP) as a non-pharmacological method for correcting physical performance. Material and methods. In the Scopus, PubMed and eLibrary databases, a selection and analysis of modern literature sources devoted to the issues of increasing human performance, especially by nonpharmacological methods, as well as the use of distant preconditioning to increase physical performance and the mechanisms for implementing this effect, were carried out. Results. Since the discovery of the phenomenon until now, researchers have considered RIP, mainly as a way to protect organs and cells from ischemic damage in clinical practice. The article presents the literature data on the use of RIP as a non-drug method for improving physical performance with single and course use cases. In addition, the article focuses on the mobilization of the body’s own resources through the mechanisms of adaptation to hypoxia developing during RIP. Conclusions. Among the non-pharmacological methods of increasing physical performance, one of the most promising, in our opinion, is RIP that mobilizes the body’s own resources through the mechanisms of adaptation to hypoxia. The advantage of the method based on short-term cessation of blood circulation in the lower extremities and subsequent reperfusion does not apply to the ways prohibited in sports, does not require the use of drugs and the availability of special equipment, signifcant costs of economic and organizational resources.

Effectiveness of Preconditioned m-Order Gauss-Seidel Method for Linear System

Focusing on the current and the proposed preconditioner, this work examines the efficacy of the preconditioned m-order Gauss-Seidel method. Type I + S and I+N preconditioning are used for the current and proposed preconditioner respectively. Preconditioning algorithms for a linear system are constructed using iterative approaches. MATLAB are used to get the findings. The effectiveness of iterative method is compared concerning convergence, condition number, determinant, spectral radius, and the number of iterations for the current and proposed preconditioner. The numerical results show that for a linear system, the preconditioned m-order Gauss-Seidel method converges at a faster rate and the proposed preconditioner succeeds where the current preconditioner fails.

Multiscale steady discrete unified gas kinetic scheme with macroscopic coarse mesh acceleration using preconditioned Krylov subspace method for multigroup neutron Boltzmann transport equation.

A multiscale steady discrete unified gas kinetic scheme with macroscopic coarse mesh acceleration [accelerated steady discrete unified gas kinetic scheme (SDUGKS)] is proposed to improve the convergence of the original SDUGKS for an optically thick system in solving the multigroup neutron Boltzmann transport equation (NBTE) to analyze the distribution of fission energy in the reactor core. In the accelerated SDUGKS, by solving the coarse mesh macroscopic governing equations (MGEs) derived from the moment equations of the NBTE, the numerical solutions of the NBTE on fine meshes at the mesoscopic level can be rapidly obtained from the prolongation of the coarse mesh solutions of the MGE. Furthermore, the use of the coarse mesh can greatly reduce the computational variables and improve the computational efficiency of the MGE. The biconjugate gradient stabilized Krylov subspace method with the modified incomplete LU preconditioner and the lower-upper symmetric-Gauss-Seidel sweeping method are implemented to solve the discrete systems of the macroscopic coarse mesh acceleration model and mesoscopic SDUGKS to further improve the numerical efficiency. Numerical solutions validate good numerical accuracy and high acceleration efficiency of the proposed accelerated SDUGKS for the complicated multiscale neutron transport problems.

An improved model order reduction method for dynamic analysis of large-scale structures with local nonlinearities

In this study, an improved model order reduction method is developed for the dynamic analysis of large-scale structures with local nonlinearities. In this method, the reduced system associated with the elements in nonlinear state is reconstructed adaptively based on the expressions of the element generalized deformation, which is defined by the eigen-decomposition of the element stiffness matrix. With the introduction of a simplified pre-conditioning method, a novel Newton iteration approach with Krylov subspace methods is proposed to solve the reduced system efficiently. Thus, dynamic analysis can be conducted efficiently for the entire structure. To expand the scope of application, an alternating iterative solution algorithm based on the model order reduction method is further developed for the structural systems simulated with both pseudo-static models and parameterized dynamic models. According to the results of numerical investigation, the novel Newton iteration approach significantly improves the solution efficiency of dynamic analysis for the large-scale structures with local nonlinearities. Meanwhile, the implementation of the alternating iterative solution algorithm contributes a new idea to the fast solution of structural systems with various types of nonlinear models.

A Preconditioned Iterative Method for a Multi-State Time-Fractional Linear Complementary Problem in Option Pricing

Fractional derivatives and regime-switching models are widely used in various fields of finance because they can describe the nonlocal properties of the solutions and the changes in the market status, respectively. The regime-switching time-fractional diffusion equations that combine both advantages are also used in European option pricing; however, to our knowledge, American option pricing based on such models and their numerical methods is yet to be studied. Hence, a fast algorithm for solving the multi-state time-fractional linear complementary problem arising from the regime-switching time-fractional American option pricing models is developed in this paper. To construct the solution strategy, the original problem has been converted into a Hamilton–Jacobi–Bellman equation, and a nonlinear finite difference scheme has been proposed to discretize the problem with stability analysis. A policy-Krylov subspace method is developed to solve the nonlinear scheme. Further, to accelerate the convergence rate of the Krylov method, a tri-diagonal preconditioner is proposed with condition number analysis. Numerical experiments are presented to demonstrate the validity of the proposed nonlinear scheme and the efficiency of the proposed preconditioned policy-Krylov subspace method.

Fast iterative solver for 3D finite-element modeling of controlled-source electromagnetic responses with vector and scalar potentials

The controlled-source electromagnetic (CSEM) forward modeling with vector and scalar potentials could provide insights into the inductive and galvanic effects. We have developed a finite-element (FE) forward modeling algorithm for the CSEM with vector and scalar potentials. The first-order vector and nodal shape functions are used for the vector and scalar potentials, respectively. To mitigate the null space and thus the nonuniqueness of the potentials caused by the curl operator, we introduce a new preconditioner constructed from an incomplete Cholesky decomposition with zero fill-ins of the Laplacian approximation to the resulted matrix after the FE discretization. We implemented a preconditioned quasiminimal residual method to iteratively solve the resulting linear system with the new preconditioner. We first verified the accuracy of the algorithm through comparison against the analytic solutions obtained for a three-layered earth model. The new iterative modeling algorithm converges much faster compared with the modeling algorithm with the preconditioner constructed from the original stiffness matrix. The efficiency and accuracy are further illustrated by comparison with the modeling scheme based on coupled potentials with explicit enforcement of the Coulomb gauge condition for the vector potential by modeling three 3D models. In addition, the accuracy of our algorithm is demonstrated via a comparison of our numerical solution for a 3D model with the numerical solution obtained from the integral equation method. We also present the inductive and galvanic components of the horizontal secondary electric field for numerical solutions obtained with direct and iterative solvers. The numerical test demonstrated that, aside from the efficiency improved with the new iterative solver, the unstable and nonuniqueness problem for the potentials is eliminated by the new preconditioner with the Laplacian approximation involved.

A new preconditioned AOR-type method for [formula omitted]-tensor equation

By using a truncated Neumann series approximation to the inverse of a given matrix, we propose a new preconditioner for improving the AOR-type method, then we develop preconditioned AOR-type methods to solve M-tensor equation and prove that the methods are convergent. Some comparison theorems are provided to show that the preconditioned AOR-type methods perform better than the AOR-type method. Finally, numerical examples illustrate that our methods are feasible and effective.

A Review of Preconditioning and Artificial Compressibility Dual-Time Navier–Stokes Solvers for Multiphase Flows

This review paper aims to summarize recent advancements in time-marching schemes for solving Navier–Stokes (NS) equations in multiphase flow simulations. The focus is on dual-time stepping, local preconditioning, and artificial compressibility methods. These methods have proven to be effective in achieving high time accuracy in simulations, as well as converting the incompressible NS equations into a hyperbolic form that can be solved using compact schemes, thereby accelerating the solution convergence and allowing for the simulation of compressible flows at all Mach numbers. The literature on these methods continues to grow, providing a deeper understanding of the underlying physical processes and supporting technological advancements. This paper also highlights the imposition of dual-time stepping on both incompressible and compressible NS equations. This paper provides an updated overview of advanced methods for the CFD community to continue developing methods and select the most suitable two-phase flow solver for their respective applications.

Computing the logarithmic capacity of compact sets having (infinitely) many components with the charge simulation method

We apply the charge simulation method (CSM) in order to compute the logarithmic capacity of compact sets consisting of (infinitely) many “small” components. This application allows to use just a single charge point for each component. The resulting method therefore is significantly more efficient than methods based on discretizations of the boundaries (for example, our own method presented in Liesen et al. (Comput. Methods Funct. Theory17, 689–713, 2017)), while maintaining a very high level of accuracy. We study properties of the linear algebraic systems that arise in the CSM, and show how these systems can be solved efficiently using preconditioned iterative methods, where the matrix-vector products are computed using the fast multipole method. We illustrate the use of the method on generalized Cantor sets and the Cantor dust.

A new preconditioned AOR method for solving multi-linear systems

In this paper, a new preconditioned AOR method for solving the multi-linear systems with -tensor is presented. The convergence of the new method and the corresponding comparison for the spectral radius of preconditioned iterative tensors are given. Numerical examples demonstrate that the new method is feasible and effective. As an application, we also show the efficiency of our preconditioner for solving higher order Markov chains.

Illumination compensation for the adjoint-state first-arrival traveltime tomography in VTI media

The sensitivity kernel of each parameter is angle-dependent in an anisotropic traveltime multiparameter inversion. To analyze the angle illumination in a transversely isotropic media with a vertical symmetry axis (VTI) by the adjoint state traveltime tomography (AST) method, a circular observation system is designed with receivers radially distributed at different propagated angles. Then, the nonuniform angular illumination in the gradient of different parameters in the VTI AST is revealed. The nonuniform angular illumination seriously hinders the simultaneous updates of multiple parameters toward the true solution and decreases the accuracy of the anisotropic multiparameter inversion. To overcome the illumination problem, a preconditioned AST method (PAST) is proposed by utilizing the diagonal elements of the approximate Hessian matrix as the angle illumination compensation for multiparameter gradients in the VTI medium. The PAST method not only compensates for angular illumination but also balances the ray density and eliminates gradient singular values, which improves the inversion accuracy for multiple parameters. The BP synthetic model test shows that the PAST method based on angular illumination compensation can invert the VTI multiparameter models more accurately. Therefore, the PAST inversion model can predict first-arrival traveltime information more accurately. Field data application in the East China Sea indicates that the inverted velocity of the proposed PAST fits well with the logging velocity, and the inverted anisotropic parameter agrees well with the Backus average values. Consequently, the image quality based on the PAST inverted models is slightly improved. It is proven that the proposed PAST method can better realize the near-surface multiparameter inversion of the VTI medium.

Differential Effects of Cytokine Versus Hypoxic Preconditioning of Human Mesenchymal Stromal Cells in Pulmonary Sepsis Induced by Antimicrobial-Resistant Klebsiella pneumoniae.

Background: Pulmonary sepsis is a leading cause of hospital mortality, and sepses arising from antimicrobial-resistant (AMR) bacterial strains are particularly difficult to treat. Here we investigated the potential of mesenchymal stromal cells (MSCs) to combat established Klebsiella pneumoniae pneumosepsis and further evaluated MSC preconditioning and pre-activation methods. Methods: The potential for naïve and preconditioned MSCs to enhance wound healing, reduce inflammation, preserve metabolic activity, and enhance bacterial killing was assessed in vitro. Rats were subjected to intratracheal K. pneumoniae followed by the intravenous administration of MSCs. Physiological indices, blood, bronchoalveolar lavage (BAL), and tissues were obtained 72 h later. Results: In vitro assays confirmed that preconditioning enhances MSC function, accelerating pulmonary epithelial wound closure, reducing inflammation, attenuating cell death, and increasing bacterial killing. Cytomix-pre-activated MSCs are superior to naïve and hypoxia-exposed MSCs in attenuating Klebsiella pneumosepsis, improving lung compliance and oxygenation, reducing bacteria, and attenuating histologic injuries in lungs. BAL inflammatory cytokines were reduced, correlating with decreases in polymorphonuclear (PMN) cells. MSCs increased PMN apoptosis and the CD4:CD8 ratio in BAL. Systemically, granulocytes, classical monocytes, and the CD4:CD8 ratio were reduced, and nonclassical monocytes were increased. Conclusions: Preconditioning with cytokines, but not hypoxia, enhances the therapeutic potential of MSCs in clinically relevant models of K. pneumoniae-induced pneumosepsis.

Multiphysics Computing of Challenging Antenna Arrays Under a Supercomputer Framework

A parallel multiphysics simulation solver is developed to solve electromagnetic-thermal-mechanical coupling for some challenging large-scale antenna arrays. To achieve high scalability of supercomputer architectures, we reconstruct the preconditioned BiCGSTAB method and the non-overlapping domain decomposition method, so that the most resource-intensive matrix factorization steps can be performed in parallel independently within subdomains. The electromagnetic and thermal fields are solved separately, while coupled through the dissipated power and the temperature-dependent material parameters; after thermal steady state is reached, the mechanical simulation is stimulated subject to the temperature rise. The accuracy of electromagnetic-thermal coupling and thermal stress solution are first validated, and then the strong/weak parallel scalability experiments of the developed multiphysics solver are performed on supercomputer. Finally, an extremely challenging antenna array is simulated using the proposed solver, where to our best knowledge we bring the scale of multiphysics simulations excited by frequency-domain electromagnetic fields to the order of billion unknowns for the first time.

Protective Efficiency Comparison of Direct and Remote Ischemic Preconditioning on Ischemia Reperfusion Injury of the Liver in Patients Undergoing Partial Hepatectomy.

Ischemia reperfusion injury greatly damages liver function and deteriorates the prognosis of patients undergoing partial hepatectomy. This study is to compare the protective efficiency of direct and remote ischemic preconditioning (DIPC and RIPC) on ischemia reperfusion injury of the liver in patients undergoing partial hepatectomy. 90 patients scheduled for partial hepatectomy were enrolled and randomly divided into control (n = 30), DIPC (n = 30), and RIPC (n = 30) groups. Baseline and surgery characteristics were collected, and ischemic preconditioning methods were carried out. Intraoperative hemodynamics, liver function and liver reserve capacity, oxidative stress, and inflammatory responses were measured, and the incidence of postoperative adverse reactions was calculated finally. 10 patients were excluded from the study, and finally, the eligible patients in three groups were 27, 28, and 25, separately. No significant differences were observed in baseline and surgery characteristics among the three groups. SBP and DBP were significantly higher after hepatic portal vein occlusion while they were significantly lower after surgery in the DIPC and RIPC groups compared with that in the control group, SBP and DBP were of great fluctuation at different time points in the control group while they showed much more stabilization in the DIPC and RIPC groups. ALT, AST, and TBIL were significantly decreased on days 1, 3, and 5 after surgery, and ICG R15 was significantly decreased while ICG K value and EHBF were significantly increased on day 1 after surgery in the DIPC and RIPC groups compared with that in the control group. Moreover, antioxidant enzyme SOD was increased, and inflammatory factors TNF-α and IL-1β were decreased 24 hours after surgery in the DIPC and RIPC groups compared with that in the control group. DIPC and RIPC also decreased hospital stays and the incidence of nausea, vomiting, and hypertension. DIPC and RIPC both alleviated ischemia reperfusion injury of the liver and reduced perioperative complications with similar protective efficiency in patients undergoing partial hepatectomy.