The annulling of the sudden appearance of an unbalance in rotary machines by using active magnetic bearings

The application of magnetic bearings has become more frequent during the last 20 years and represents a significant aspect of improvements in the construction of machines with rotary motion. With the advancement of technology, the number of applications in which magnetic bearings have found their application is increasing. In this paper, it is shown how the effect of magnetic forces can annul the negative influence of unbalance, which suddenly appeared in a rotor supported in active magnetic bearings. Such cases may occur in operation due to breakage and rotor parts falling off (e.g., fan blades), which will lead to a sudden change in the mass balance of the rotor system and dislocation of the centre of mass in relation to the geometric centre of the rotor. In the paper, a mathematical model of the dynamic behaviour of a rigid rotor in active magnetic bearings was developed. The model is nonlinear and has five degrees of freedom and can only be solved numerically. The Newmark beta method and the Newton-Raphson method were used to solve the system of nonlinear differential equations. The results of the simulation showed the advantages of using active magnetic bearings for annulling sudden occurrences of unbalance in rotary machines

Implementing Lensless Cameras in Autonomous Robotic Systems

The open-source Robot Operating System (ROS) is a mixed and scalable P2P network-based robotics framework. We examine lensless compressive imaging using a hardware apparatus assembly having an imaging sensor, but no lens. Cameras with lenses have been the standard, but several factors constrain their application. Lensless cameras may reduce the cost, size, and weight of image processing as we move away from use of expensive lenses in robot designs. Lensless cameras can be used also in applications such medicine, where apparatus size is very important. To support our objective we show how ROS applications are developed and most importantly how one can build applications that allows users to complete useful tasks in a timely manner with high performance

Immigrants in ELT Books

The aim of this paper is to provide a brief overview of how immigrants are depicted in modern ELT books and how frequently they appear in them. In order to address this issue we analyzed a random sample of most frequently used ELT books and briefly described immigrant-related content. Immigrants do appear in all books we analyzed, although there are certain differences in how frequently they appear and in the ways in which they are described. The only common feature of these books is that they offer almost identical pictures of modern society and multiculturalism

The application of parameter sensitivity analysis methods to inverse simulation models

Knowledge of the sensitivity of inverse solutions to variation of parameters of a model can be very useful in making engineering design decisions. This paper describes how parameter sensitivity analysis can be carried out for inverse simulations generated through approximate transfer function inversion methods and also by the use of feedback principles. Emphasis is placed on the use of sensitivity models and the paper includes examples and a case study involving a model of an underwater vehicle. It is shown that the use of sensitivity models can provide physical understanding of inverse simulation solutions that is not directly available using parameter sensitivity analysis methods that involve parameter perturbations and response differencing

Chemically Recyclable and Upcyclable Epoxy Resins Derived from Vanillin

Epoxy resins constitute a very significant portion of all high-performance plastics due to their excellent thermal and mechanical properties that appear in a wide range of applications. Nevertheless, traditional epoxy networks show limitations regarding chemical recycling due to their covalently crosslinked structures. The current methods to recycle epoxy resins are not indeed through sustainable ways, but this issue could be solved by developing smart monomers with functional groups, which can be switched between polymerized and depolymerized states. Herein, we developed two bio-based liquid monomers based on vanillin structures containing aldehyde, acetal, and oxirane-ring functionalities. These monomers were polymerized in solvent-free conditions using commercially available diamines, resulting in double-dynamic imine-acetal-containing thermosets. These networks combine the excellent properties of the traditional epoxy systems and dynamic polymers. Most importantly, such thermosets were fully depolymerized into vanillin, which can be reused for the preparation of original epoxy monomers, and a mixture of well-defined polyols, which was upcycled into high-performance polyurethane

An Efficient Itemset Representation for Mining Frequent Patterns in Transactional Databases

In this paper we propose very efficient itemset representation for frequent itemset mining from transactional databases. The combinatorial number system is used to uniquely represent frequent k-itemset with just one integer value, for any k ≥ 2. Experiments show that memory requirements can be reduced up to 300 %, especially for very low minimal support thresholds. Further, we exploit combinatorial number schema for representing candidate itemsets during iterative join-based approach. The novel algorithm maintains one-dimensional array rank, starting from k = 2nd iteration. At the index r of the array, the proposed algorithm stores unique integer representation of the r-th candidate in lexicographic order. The rank array provides joining of two candidate k-itemsets to be O(1) instead of O(k) operation. Additionally, the rank array provides faster determination which candidates are contained in the given transaction during the support count and test phase. Finally, we believe that itemset ranking by combinatorial number system can be effectively integrated into pattern-growth algorithms, that are state-of-the-art in frequent itemset mining, and additionally improve their performances

Free vibrations of planar serial frame structures in the case of axially functionally graded materials

This paper considers the problem of modal analysis and finding the closed-form solution to free vibrations of planar serial frame structures composed of Euler-Bernoulli beams of variable cross-sectional geometric characteristics in the case of axially functionally graded materials. Each of these beams is performing coupled axial and bending vibrations, where coupling occurs due to the boundary conditions at their joints. The numerical procedure for solving the system of partial differential equations, after the separation of variables, is reduced to solving the two-point boundary value problem of ordinary linear differential equations with nonlinear coefficients and linear boundary conditions. In this case, it is possible to transfer the boundary conditions and reduce the problem to the Cauchy initial value problem. Also, it is possible to analyze the influence of different parameters on the structure dynamic behavior. The method is applicable in the case of different boundary conditions at the right and left ends of such structures, as illustrated by an appropriate numerical example

Free vibrations of planar serial frame structures in the case of axially functionally graded materials

This paper considers the problem of modal analysis and finding the closed-form solution to free vibrations of planar serial frame structures composed of Euler-Bernoulli beams of variable cross-sectional geometric characteristics in the case of axially functionally graded materials. Each of these beams is performing coupled axial and bending vibrations, where coupling occurs due to the boundary conditions at their joints. The numerical procedure for solving the system of partial differential equations, after the separation of variables, is reduced to solving the two-point boundary value problem of ordinary linear differential equations with nonlinear coefficients and linear boundary conditions. In this case, it is possible to transfer the boundary conditions and reduce the problem to the Cauchy initial value problem. Also, it is possible to analyze the influence of different parameters on the structure dynamic behavior. The method is applicable in the case of different boundary conditions at the right and left ends of such structures, as illustrated by an appropriate numerical example