3D discrete element modeling of concrete: study of the rolling resistance effects on the macroscopic constitutive behavior

The Discrete Element Method (DEM) is appropriate for modeling granular materials [14] but also cohesive materials as concrete when submitted to a severe loading such an impact leading to fractures or fragmentation in the continuum [1, 5, 6, 8]. Contrarily to granular materials, the macroscopic constitutive behavior of a cohesive material is not directly linked to contact interactions between the rigid Discrete Elements (DE) and interaction laws are then defined between DE surrounding each DE. Spherical DE are used because the contact detection is easy to implement and the computation time is reduced in comparison with the use of 3D DE with a more complex shape. The element size is variable and the assembly is disordered to prevent preferential cleavage planes. The purpose of this paper is to highlight the influence of DE rotations on the macroscopic non-linear quasi-static behavior of concrete. Classically, the interactions between DE are modeled by spring-like interactions based on displacements and rotation velocities of DE are only controlled by tangential forces perpendicular to the line linking the two sphere centroids. The disadvantage of this modeling with only spring-like interactions based on displacements is that excessive rolling occurs under shear, therefore the macroscopic behavior of concrete is too brittle. To overcome this problem a non linear Moment Transfer Law (MTL) is introduced to add a rolling resistance to elements. This solution has no influence on the calculation cost and allows a more accurate macroscopic representation of concrete behavior. The identification process of material parameters is given and simulations of tests performed on concrete samples are shown

Investigation of the Kinetic Model for the Process of Liquid Drops Formation in the Form of Capsule

Capsulation as a technological principle can provoke an activation of innovative activity in food branch and become a cause of elaboration and introduction of new scientifically grounded technologies of raw material processing, creation of new commodity forms, comfortable in consumption, increase of production volumes and effectiveness of food production use, elaboration and application of the modern principally new technologies, technological processes, methods and equipment that in common can essentially influence the state and development of food technologies.The model of capsulation of liquids of different origin by extrusion method was elaborated taking into account the regularities of gravitation and using the methods of system analysis. Kinetics of capsule structure creation, regularities of getting round forms with different diameter were determined. The gotten regularities are the base of scientific-technological principles of getting oil-fat production, capsulated with thermo- and acid-stable properties. It was theoretically proved, that the main factor that limits the process of drop formation and separation is a stage of formation of embryo and drop itself. The time of embryo and drop formation is much more (in 20 times approximately) than the time of bridge rupture. The presence of coat of capsulated liquids essentially influences the sizes of bridge and drop and the time of processes of drop formation and separation. At that, the increase of relative coefficient of surface tension in 3 times increases a drop radius in 1,6 time and full time of drop formation and separation in 2,5 times. The received equations can be used for experimental verification of the offered model of liquid drop formation and separation

Vector Reachability Problem in SL(2,Z)

This paper solves three open problems about the decidability of the vector and scalar reachability problems and the point to point reachability by fractional linear transformations over finitely generated semigroups of matrices from . Our approach to solving these problems is based on the characterization of reachability paths between vectors or points, which is then used to translate the numerical problems on matrices into computational problems on words and regular languages. We will also give geometric interpretations of these results

The Identity Problem for Matrix Semigroups in SL2(Z) is NP-complete

In this paper, we show that the problem of determining if the identity matrix belongs to a finitely generated semigroup of $2\times 2$ matrices from the modular group $\text{PSL}_2(\mathbb Z)$ and thus the Special Linear group $\text{SL}_2(\mathbb Z)$ is solvable in $\mathbf{NP}$. From this fact, we can immediately derive that the fundamental problem of whether a given finite set of matrices from $\text{SL}_2(\mathbb Z)$ or $\text{PSL}_2(\mathbb Z)$ generates a group or free semigroup is also decidable in $\mathbf{NP}$. The previous algorithm for these problems, shown in 2005 by Choffrut and Karhum\"aki, was in \EXPSPACE mainly due to the translation of matrices into exponentially long words over a binary alphabet $\{s,r\}$ and further constructions with a large nondeterministic finite state automaton that is built on these words. Our algorithm is based on various new techniques that allow us to operate with compressed word representations of matrices without explicit expansions. When combined with the known $\mathbf{NP}$-hard lower bound, this proves that the membership problem for the identity problem, the group problem and the freeness problem in $\text{SL}_2(\mathbb Z)$ are $\mathbf{NP}$-complete

Time Response of Shape Memory Alloy Actuators

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Force/displacement actuators with the high output power and time response can be fabricated from shape memory wires or ribbons. Typically Ni-Ti shape memory alloys are used as an active material in such actuators. They are driven by Joule heating and air convection cooling. In the present work, the time response of various types of Ni-Ti actuators having different transformation temperatures and geometrical sizes, is studied systematically under conditions of free and forced air convection. The simple analytical model for calculating the time response is developed which accounts for the latent heat and thermal hysteresis of transformation. For all the types of considered actuators, the calculated time response is in a good agreement with that observed experimentally. Finally, on the base of the suggested model, we present the time response of Ni-Ti actuators calculated as a function of their transformation temperature and cross section dimensions

What do teens make of personal informatics? Youth responses to self-tracking practices within a classroom setting

Personal informatics (PI) technologies allow users to collect data about aspects of their lifestyle like mood or step count. Though teens increasingly encounter and use such technologies, little is known about how they ascribe meaning to their own PI activities. We report a qualitative study of the PI experiences of eighteen teens (aged 14 – 17). Following a learning phase focused on interpreting PI data, participants chose a personal goal that interested them and a PI tool to track it for 4-8 weeks in everyday contexts. Participants proved to be competent, flexible users of PI tools, tracking a range of meaningful life factors, from ‘worries’ to ‘exercise’; they valued learning about ‘natural patterns’ in their lives and were motivated to manage their emotions and evaluate whether they were doing the right thing. Our findings contribute to understanding how young people can engage in appropriation and interpretation of PI data – suggesting opportunities for educational interventions and design

What do Teens Make of Personal Informatics?: Young People's Responses to Self-Tracking Practices for Self-Determined Motives

Personal informatics (PI) technologies allow users to collect data about aspects of their lifestyle like mood or step count. Though teens increasingly encounter and use such technologies, little is known about how they ascribe meaning to their own PI activities. We report a qualitative study of the PI experiences of eighteen teens (aged 14 – 17). Following a learning phase focused on interpreting PI data, participants chose a personal goal that interested them and a PI tool to track it for 4-8 weeks in everyday contexts. Participants proved to be competent, flexible users of PI tools, tracking a range of meaningful life factors, from ‘worries’ to ‘exercise’; they valued learning about ‘natural patterns’ in their lives and were motivated to manage their emotions and evaluate whether they were doing the right thing. Our findings contribute to understanding how young people can engage in appropriation and interpretation of PI data – suggesting opportunities for educational interventions and design

The Determination of the Competent Court When Applying for Judicial Protection in an Administrative Offense Case

The problem of determining the competence of the court to consider a complaint (application) when applying for judicial protection of a person held liable in an administrative offense case, both by the person himself and by the judges, is considered. The study of existing rules of law, judicial acts of courts of first and higher instances, including the Supreme Court of the Russian Federation, the Constitutional Court of the Russian Federation, the analysis of scientific works devoted to the problem of determining the competent court both in cases of administrative offenses and in civil proceedings is a method, which allows one to study the problem of possible restriction or exclusion of access to judicial protection of persons held administratively liable, when appealing against the relevant regulatory act recognizing them as such. The Author compares the legislation on judicial proceeding in cases of administrative offenses of the Russian Federation and the Republic of Belarus. Investigates the procedure for appealing against a decision in a case on an administrative offense and a decision within the framework of the Code of the Russian Federation on Administrative Offenses and the Arbitration Procedure Code of the Russian Federation, their similarities and differences in the regulation of the appeal procedure. Court practice is brought to attention, which clearly demonstrates the essence of the problem of determining the competent court when applying for judicial protection in a case of an administrative offense. Judicial practice demonstrates a variety of approaches to the existing problem not only by the same court, but also by the same judge. The rights of persons brought to administrative responsibility, violated due to the existence of this problem, are identified. Through the study of scientific works of civil procedure scholars, the Author discusses the possibility of changing existing legislation in order to eliminate the possibility of depriving a person brought to administrative responsibility of the right to judicial protection. The Author proposes to exclude a number of norms from the current legislation, while the norms governing the issue of competence should be changed in terms of the procedure for handling an application received by the court, a complaint in a case of an administrative offense. The importance of resolving this problem for the Russian Federation as a legal state, which is the Russian Federation, is explained