On the development and performance of multitime-step coupling methods for transient multiscale problems

An ever-increasing number of scientific and engineering applications require modeling and computer simulation of coupled (interaction-type) problems. In such problems, disparate spatial and temporal scales are present because of the occurrence of different physical phenomena. This feature renders the task of developing numerical methods for simulation of coupled problems rather challenging. In the past few decades, many attempts have been devoted to study the computational aspects of coupled problems. However, majority of them suffer from stability and convergence issues. Limitations on number of subdomains and time steps are some of the other drawbacks. Our aim, in this poster presentation, is to identify the main causes of the aforementioned restrictions. Furthermore, we will introduce a Differential/Algebraic Equation (DAE) perspective towards coupled problems. A new computational framework [1] based on the theory of DAEs will be presented that allows arbitrary number of subdomains, different time steps, time integrators, and different numerical formulations in different regions of the computational domain. These methods will be shown to be stable and accurate. Several numerical examples will be shown to demonstrate the versatility and performance of the proposed framework. REFERENCE [1] Karimi, S. and Nakshatrala, K.B. On multi-time-step monolithic coupling algorithms for elastodynamics. arXiv:1305.6355, 2013

Monolithic multitime-step coupling methods for transient problems in solid mechanics and transport

Developing computational frameworks for transient interaction-type problems (e.g. fluid–structure interaction, thermal–structure interaction) has been an active area of research in the past few decades. Computer simulation of such systems is extremely important in state-of-the-art science and engineering applications. Coupled problems often feature disparate temporal and spatial scales due to the presence of different physical phenomena. Hence, a desirable numerical framework should be able to facilitate different numerical formulations, different -time--integrators, and time-steps in different regions of the computational domain. However, till date, no comprehensive numerical framework exists. Many of the coupling methods suffer from stability and convergence issues. Some other common drawbacks are limitation on the number of subdomains, time-steps, and preferential -treatment of subdomains. In this presentation, we shall take a theoretical point of view (based on theory of differential/algebraic equations) toward coupled problems. We shall shed light on the cause of deficiencies in some of the earlier notable works. The proposed multitime-step coupling method [1] allows arbitrary number of subdomains, different finite element formulations, and different time-integrators and time-steps in different spatial regions. A comprehensive theoretical study of this method (which includes stability, influence of perturbations, bound on drifts, accuracy, and numerical energy dissipation properties) will be presented. Several numerical examples ranging from simple test problems to elastodynamics and advective–diffusive–reactive systems will be presented. These problems will provide a valuable insight into attractive features of the proposed method and will showcase its performance. REFERENCE [1] Karimi, S. Nakshatrala, K.B. On Multi-time-step Monolithic Coupling Algorithms for Elastodynamics. arXiv:1305.6355, 2013

Computational Methods for Multi-Scale Temporal Problems: Algorithms, Analysis, and Numerical Experiments

A major challenge in numerical simulation of most natural phenomena is the presence of disparate temporal and spatial scales. Capturing all the fine features can be computationally prohibitive. Hence, development of efficient and accurate multi-scale numerical algorithms has gained immense attention from engineers and scientists. Typically, a single numerical method cannot efficiently capture all the aforementioned features. Due to the assumptions made in construction of numerical methods and mathematical models, the range of applicability to various length and time-scales is often limited. A direction in resolving this issue is to apply different numerical methods in different regions of the computational domain. This strategy enables computation of necessary details as desired by the user. In this work, we propose numerical methodologies based on domain partitioning techniques that allow different time-steps and time-integrators in different regions of the computational domain. The first problem of interest is elastodynamics, which can pose various temporal scales in impact, contact and wave propagation problems. A monolithic (strong) coupling algorithm based on non-overlapping domain partitioning is proposed. The proposed algorithm is based on the theory of differential/algebraic equations and its numerical stability, energy conservation and accuracy is studied in detail. Following these findings, we extend this algorithm to advection-diffusion-reaction problems. The proposed algorithm proves useful especially in cases where the relative strength of the involved processes changes dramatically with respect to spatial coordinates. Numerical stability and accuracy of this method is studied and its application to fast bimolecular chemical reactions is showcased. Further on, we confine our attention to single and multiple-relaxation-time lattice Boltzmann methods for the advection-diffusion equation and study their performance in preserving the maximum principle and the non-negative constraint. Finally, a computational framework based on overlapping domain decomposition methods is proposed. This framework is designed for advection-diffusion problems and allows coupling of the finite element method and lattice Boltzmann methods with different time-steps and grid sizes. Additionally, a new method for enforcing the Dirichlet and Neumann boundary conditions on the numerical solution from the lattice Boltzmann method is proposed. This method is based on maximization of entropy and ensures non-negativity of the discrete distributions on the boundary of the domain. We study the performance of this framework through numerical experiments and showcase its application to fast and equilibrium chemical reactions.Civil and Environmental Engineering, Department o

The role of banks in the realization of resistive economy goals

This article tries to study and identify the internal and external structural problems of Iran monetary and bank system and the role of banks in the resistive economy with respect to the significance of resistive economy and its requirements. And, this has made an attempt to present useful information on this type of economy and the improvement of the monetary system structure of Iran. The results of the article concerning the identification of the challenges in the monetary and banking system in Iran, that is, the only existing solution in resistive economy are the removal of damages and reconstruction of the inefficient and tired structures. Reformation of some economic policy making in Iran as well as principle and rational planning is regarded

The role and position of organizational culture in knowledge management in government-owned banks of Gilan Province

The purpose of this paper is to investigate the relationship between two variables of organizational culture and knowledge management in government-owned banks of Gilan Province. Studies that deal with reasons of the failure of management innovations suggest that organizational culture is a major factor for success. The research method is a descriptive correlational. Research population includes 346 employees of government-owned banks of Gilan Province. The measuring instrument is questionnaire and data are analyzed by SPSS software, t statistical tests and Spearman correlation test. Results showed that there was a significant relationship between organizational culture and knowledge management; and between the components, the organizational culture of individual creativity is most correlated with knowledge management

The role and position of organizational culture in knowledge management in government-owned banks of Gilan Province

The purpose of this paper is to investigate the relationship between two variables of organizational culture and knowledge management in government-owned banks of Gilan Province. Studies that deal with reasons of the failure of management innovations suggest that organizational culture is a major factor for success. The research method is a descriptive correlational. Research population includes 346 employees of government-owned banks of Gilan Province. The measuring instrument is questionnaire and data are analyzed by SPSS software, t statistical tests and Spearman correlation test. Results showed that there was a significant relationship between organizational culture and knowledge management; and between the components, the organizational culture of individual creativity is most correlated with knowledge management

The role of banks in the realization of resistive economy goals

This article tries to study and identify the internal and external structural problems of Iran monetary and bank system and the role of banks in the resistive economy with respect to the significance of resistive economy and its requirements. And, this has made an attempt to present useful information on this type of economy and the improvement of the monetary system structure of Iran. The results of the article concerning the identification of the challenges in the monetary and banking system in Iran, that is, the only existing solution in resistive economy are the removal of damages and reconstruction of the inefficient and tired structures. Reformation of some economic policy making in Iran as well as principle and rational planning is regarded

The role of banks in the realization of resistive economy goals

This article tries to study and identify the internal and external structural problems of Iran monetary and bank system and the role of banks in the resistive economy with respect to the significance of resistive economy and its requirements. And, this has made an attempt to present useful information on this type of economy and the improvement of the monetary system structure of Iran. The results of the article concerning the identification of the challenges in the monetary and banking system in Iran, that is, the only existing solution in resistive economy are the removal of damages and reconstruction of the inefficient and tired structures. Reformation of some economic policy making in Iran as well as principle and rational planning is regarded

Antiplatelet therapy and exodontia: far away from a definite conclusion

Dear Editor;We read a review article about antiplatelet therapy and dental management in your journal (1). Kumar concluded that patients taking dual antiplatelet therapy has an increased risk for post-operative bleeding complications.The focus question of this article contains many other smeller questions. We recently answered one of these questions in our study; one tooth extraction is safe in patients taking aspirin and clopidogrel during one year after percutaneous coronary intervention (PCI) with stenting (2). But many questions remained without answer. Is two teeth extraction safe in these patients? What about more than two teeth extraction or in patients taking other antiplatelet drugs for other indications? What about other dental interventions? For answering each of these specific questions we need to design a prospective original study, with enough sample size, and comparing the results with a matched control group.Also there are many confounders for bleeding after exodontia (e.g. dentist's skill, type of antiplatelet drug and its manufacturing company, indication and duration of taking antiplatelet therapy, number and kind of extracted teeth, and dentist's skill) (2, 3). Controlling these confounders needs prospective studies focusing on specific group of patients. For example, patients taking unique dose and type of antiplatelet drug for a unique indication and duration, undergoing unique dental intervention by unique dentist. Then this result could be compared with a group of healthy subjects undergoing same dental intervention by the same dentist. So we do not have enough evidences to make a definite conclusion about what we should do in case of dental intervention for patients taking antiplatelet therapy.Â

The relationship between proactive personality and employees’ creativity: the mediating role of intrinsic motivation and creative self-efficacy

Employees’ creativity is one of the most important factors in the success of organizations which has attracted the attention of researchers in recent years. Recent research has suggested that proactive personality fosters creativity. However, there is a lack of research into the mechanisms that make this link possible. The main purpose of this study was to examine the relationship between proactive personality and employee creativity by focusing on the mediating roles of intrinsic motivation and creative self-efficacy. Data from 178 Iranian agriculture experts were collected and analyzed by conducting structural equation modeling. The results indicated that proactive personality was directly and positively related to employees’ creativity. Additionally, the results showed that intrinsic motivation and creative self-efficacy partially mediated the relationship between proactive personality and employees’ creativity. The findings not only shed light on mechanisms that underlie in the proactive personality -creativity linkage but they also highlight the importance of intrinsic motivation and creative self-efficacy in the linkage. Together, the study extends the effect of proactive personality on creativity and the mediation mechanisms underlying this relationship. The theoretical and practical implications, limitations, and future research directions are discussed