Modeling anisotropic and rate-dependent plasticity in short-fiber reinforced thermoplastics

In this study, an anisotropic viscoelastic-viscoplastic macro-mechanical model is presented for short-fiber reinforced thermoplastics (SFRT). In injection molding of SFRT, the fiber orientation is influenced by the flow velocity profile which varies throughout the mold. The flow-induced orientation in the microstructure leads to anisotropy in the mechanical response. In addition to the mechanical anisotropy, SFRTs show time dependent behavior because of the thermoplastic matrix. The developed model captures the effects of both material orientation and loading rate on the yield behavior. In this study, uniaxial tests are performed at different strain rates and material orientations with samplescutfrominjectionmoldedplaques. Theexperimentalresultsshowthattheeffects of loading rate and material orientation on the yield are decoupled. The presented model takes advantage of this observation to simplify material characterization. An implicit integration scheme is used for the numerical implementation of the model as a UMAT in ABAQUS. Multiple relaxation times are used in order to capture the nonlinear pre-yield regime. An efficient method for obtaining the model parameters for different modes is proposed. Experimental results are used for validation of the model and a good agreement is observed for the prediction of viscoelastic and viscoplastic behavior

Irradiation-induced confinement in a quasi-one-dimensional metal

The anisotropic resistivity of PrBa$_2$Cu$_4$O$_8$ has been measured as a function of electron irradiation fluence. Localization effects are observed for extremely small amounts of disorder corresponding to electron mean-free-paths of order 100 unit cells. Estimates of the localization corrections suggest that this anomalous localization threshold heralds a crossover to a ground state with pronounced one-dimensional character in which conduction electrons become confined to a small cluster of chains.Comment: 4 pages, 4 figure

Possible co-existence of local itinerancy and global localization in a quasi-one-dimensional conductor

In the chain compound PrBa$_2$Cu$_4$O$_8$ localization appears simultaneously with a dimensional crossover in the electronic ground state when the scattering rate in the chains exceeds the hopping rate between the chains. Here we report the discovery of a large, transverse magnetoresistance in PrBa$_2$Cu$_4$O$_8$ in the localized regime. This result suggests a novel form of localization whereby electrons retain their metallic (quasi-one-dimensional) character over a microscopic length scale despite the fact that macroscopically, they exhibit localized (one-dimensional) behavior.Comment: 4 pages, 4 Figure

Enhancing synchronizability of weighted dynamical networks using betweenness centrality

By considering the eigenratio of the Laplacian of the connection graph as synchronizability measure, we propose a procedure for weighting dynamical networks to enhance theirsynchronizability. The method is based on node and edge betweenness centrality measures and is tested on artificially const ructed scale-free, Watts-Strogatz and random networks as well as on some real-world graphs. It is also numerically shown that the same procedure could be used to enhance the phase synchronizability of networks of nonidentical oscillators

The Effect of Robotic Education on Problem-Solving Skills of High School Students in Physics

Background and Objective: Increasing development of technology has led to appearance of machines calls robots which have influenced different dimensions of human life. Robotics is one of the newest technologies in today’s world that has a great role in industry today and is gradually expanding throughout human life. Robotics is a new tool that can meet many human needs and influence the attitudes and thoughts of people, especially adolescents, and influence their behavior, because adolescents are interested in gaining new experiences and technology, due to new inventions such as robotics, this need is met. Students feel more comfortable with technology and robotics, because this technology quenches their curiosity. The world of robotics is a combination of electronics, mechanics, software and hardware that is constantly evolving. In other words, a robot is an electromechanical device or intelligent software to replace humans, with the aim of performing various tasks. A machine that can be programmed to execute various commands or perform a series of special tasks, especially those that are beyond the natural capabilities of men. Robotics, due to its interdisciplinary nature, has an attractive approach to education, because it requires expertise in the fields of mathematics and aesthetics, while mathematics strengthens problem-solving thinking and aesthetics strengthens creative thinking. Therefore, it can be said that robotics is effective on students' problem-solving and creative thinking. This study aims to evaluate the effect of robotic education on problem-solving of junior-high school students in physics. Methods: This is a semi-experimental and causal-comparative study. The statistical population includes all schools participating in the robotics training program in Tehran. Using cluster sampling, from 5 districts of Tehran, one district was chosen, and then randomly from its schools, 6 schools with 173 students were selected and 120 students were randomly selected among them. Research tools included a researcher-made questionnaire of problem-solving measurement and an educational package of robotic structures in physics. Its validity was confirmed by content validity method by robotics experts and testers and its reliability was achieved 0.95 using Cronbach's alpha. For data analysis, SPSS software was used in two levels of descriptive statistics (indexes of centrality and frequency) and deductive statistics (independent t-test, variance analysis and covariance analysis). Findings: The findings show there is a significant relationship between educational robotic and problem-solving skills, and also, there is no significant relationship between the effect of robotic education on the level of problem-solving skills among girls and boys students. Conclusion: Robotic education has a significant effect on problem solving skills of high school students. The present study, like any other research, has certain limitations such as using only one research instrument, i.e. questionnaire and not using other instruments and geographical and curricular limitations and training costs and robot construction, and need for advanced workshop equipment. There was a lack of original and standard software. Therefore, it is suggested that the present study be conducted in other geographical areas and in other courses and in places with advanced engineering facilities to increase the probability of generalizations. Based on the findings of this study, it is suggested that arrangements be made to investigate the effect of robotics on students' motivation and learning, and to provide accurate information to provide solutions for the correct use of robotics training. In addition, it is suggested that robotics training methods in other countries be considered to promote the effectiveness of robotics training on students.   ===================================================================================== COPYRIGHTS  ©2020 The author(s). This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, as long as the original authors and source are cited. No permission is required from the authors or the publishers.  ====================================================================================

Opioids and viral infections: A double-edged sword

Opioids and their receptors have received remarkable attention because they have the ability to alter immune function, which affects disease progression. In vitro and in vivo findings as well as observations in humans indicate that opioids and their receptors positively or negatively affect viral replication and virus-mediated pathology. The present study reviews recent insights in the role of opioids and their receptors in viral infections and discusses possible therapeutic opportunities. This review supports the emerging concept that opioids and their receptors have both favorable and unfavorable effects on viral disease, depending on the type of virus. Targeting of the opioid system is a potential option for developing effective therapies; however caution is required in relation to the beneficial functions of opioid systems. © 2016 Tahamtan, Tavakoli-Yaraki, Mokhtari-Azad, Teymoori-Rad, Bont, Shokri and Salimi

Faunistic study on hover flies (Diptera:Syrphidae) in the eastern part of Zanjan province, Iran

Abstract In order to study on Syrphidae faunistic in the eastern part of Zanjan province in the years of 2008 and 2009, some adult specimens were collected and identified. In total, 31 species belong to 16 genus from 2 subfamilies were collected. Among the specimens, 28 species as follow are new records for Zanjan province and the species marked with an asterisk is the first record from Iran

Validating the motivational model for web- based Teaching

The purpose of this study was the external validation of the motivational model for web-based instruction with emphasis on the role of the teacher. The proposed model is based on self-determination theory and consists of three main categories (social presence, cognitive engagement, management) and nine sub-categories. In this quasi–experimental study, a pretest–posttest design with a control group was used. The population included all the undergraduate students of Kharazmi University (Karaj Campus) in the academic year 2015-2016. Of these, 44 students were selected through a random sampling procedure and were randomly assigned to either of experimental and control groups. Both groups participated in training course of communication skills. The instrument was Haller’s Situational Motivational scale that assesses four constructs of the self-determination theory (intrinsic motivation, identified regulation, external regulation, and amotivation). Analysis of covariance (ANCOVA) was used to analyze the gathered data. The results showed that the proposed model can improve the learners' intrinsic motivation in web-based learning environment and can be a basis for teaching in virtual courses