Process of extrusion in the unit of special design

Extrusion of paste materials is a means of processing powder materials to a granulated form. A powder material is mixed with a liquid and transformed to the form of paste. The paste has to have the appropriate flow properties to be able to be extruded. This is very important especially in the area of reduction between the barrel and die. There is the place where the paste has to deform itself and to flow into the holes of die that have a smaller cross section than is in the barrel. It is the zone where the rheology properties of paste and its speed have the biggest influence on the extrusion pressure. It can even happen that the paste can be dewatered under the pressure gradient in this place. If the rotor with blades is situated in this zone it has a positive influence on the process of extrusion. This element has an influence on the rate of shear strain and decreasing of the apparent viscosity with a following drop in the extrusion pressure. This paper describes research of the process of extrusion in equipment with separated drives of the screw and a rotor that is placed in the input zone in the hole of matrix. First influence of the operating speeds of screw and rotor on extrusion pressure is studied here, then it is compared with the torque that is needed for the drive of the rotor. According to the results it is evident that the extrusion pressure increases with the accrual of the speed of flowing paste and decreases with the increase of the rotors operating speed. The influence of flowing paste on the torque is complicated. There is an interval where the torque goes up and then an interval in which the torque decreases. The results of experiments confirmed that the rotor has a positive influence on the process of extrusion.We would like to thank the Grant Agency of the Slovak Republic for supporting our research work performed in the frame of Grant Project No.1/8092/01.     

Integrating Guidance into Relational Reinforcement Learning

Reinforcement learning, and Q-learning in particular, encounter two major problems when dealing with large state spaces. First, learning the Q-function in tabular form may be infeasible because of the excessive amount of memory needed to store the table, and because the Q-function only converges after each state has been visited multiple times. Second, rewards in the state space may be so sparse that with random exploration they will only be discovered extremely slowly. The first problem is often solved by learning a generalization of the encountered examples (e.g., using a neural net or decision tree). Relational reinforcement learning (RRL) is such an approach; it makes Q-learning feasible in structural domains by incorporating a relational learner into Q-learning. The problem of sparse rewards has not been addressed for RRL. This paper presents a solution based on the use of reasonable policies to provide guidance. Different types of policies and different strategies to supply guidance through these policies are discussed and evaluated experimentally in several relational domains to show the merits of the approach.     

Elastodynamic near-tip fields for a crack propagating along the interface of two orthotropic solids

The elastodynamic stress field near a crack tip rapidly propagating along the interface between two dissimilar orthotropic elastic solids is solved numerically, for in-plane motion. The cartesian displacements are sought in the separated forms, $\text{r}{}^{\mathrm{p}}\text{U(θ)}$ and $\text{r}{}^{\mathrm{p}}\text{V(θ)}$, $\text{r}$ and θ being polar coordinates centered at the moving tip. This reduces the mathematical statement of the problem to two complex second-order linear ordinary differential equations for complex functions $\text{U(θ)}$ and $\text{V(θ)}$. By means of the finite difference method, a matrix eigenvalue problem of the type $\text{ΣA}{}_{\mathrm{ij}}\text{(p)X}{}_{\mathrm{j}}\text{= 0}$, is obtained where $\text{A}{}_{\mathrm{ij}}\text{(p)}$ are polynomials of the complex variable $\text{p}$ and $\text{X}{}_{\mathrm{j}}$, are complex unknowns. An iterative numerical scheme for determining $\text{Im(p)}$ is developed and the roots $\text{p}$ as well as angular stress and displacement distributions are calculated and plotted for various material combinations. Comparison with exact solutions for the case of dissimilar Isotropie solids indicates good accuracy of the numerical solution. The orthotropic nature of the materials is shown to have a significant effect on stress maximums.     

Finite element program for moisture and heat transfer in heated concrete

A new axisymmetric finite element program for the analysis of pore pressure, moisture content and temperature in heated concrete is described. The program is based on the diffusion equations for coupled heat and moisture transfer and uses a step-by-step time integration. The finite element scheme is based on Galerkin method. For time integration a step-by-step solution with iterations is used. The numerical analysis is complicated by the fact that the sorption isotherms exhibit a steep jump at saturation-nonsaturation transitions, and that the permeability dependence on temperature exhibits a jump of two orders of magnitude at 100°C. The mathematical model takes into account the release of chemically bound water due to dehydration and the associated changes in the pore space. The program may also be used at normal temperatures. Predictions of the program are compared with tests by HEDL as well as two other existing programs.     

Modelling Highly Inflected Slovenian Language

This paper concerns the development of statistical language models of the Slovenian language for use in an automatic speech recognition system. The proposed techniques are language-independent and can be applied to other highly inflected Slavic languages. The large number of unique words in inflected languages is identified as the primary reason for performance degradation. This article discusses the concept of word-formation in the Slovenian language, which is also common to all Slavic languages. The main problems are outlined for word-based language models. A novel variation on the N-gram modelling theme is examined where, instead of using words, modelling units are chosen to be stems and endings. Only data-driven algorithms are employed, which decompose words automatically. A significant reduction in the OOV rate results when using stems and endings for modelling the Slovenian language. The final part of this article focuses on building a speech recogniser. Two different decoding strategies have been employed: one-pass and two-pass search decoders. Language modelling experiments have been performed using the VEER newswire text corpus, and recognition experiments have been conducted using the SNABI Slovenian speech database. The new language model resulted in the reduction of the OOV rate by 64%, and the recognition accuracy was improved by 4.34%.     

A characterisation of thick film resistors for strain gauge applications

Some commercial thick film resistors with sheet resistivities from 1 kohm/sq. up to 1 Mohm/sq. were evaluated for strain gauge applications. Temperature coefficients of resistivity, noise indices and gauge factors (GFs) were measured. For the same resistor series GFs and noise indices increase with increasing sheet resistivity. However, both GFs and noise indices are different for resistors with the same nominal sheet resistivity but from different resistor series. The results indicated that the microstructure rather than the different chemical composition of the conductive phase in thick film resistors is the primary reason for the different gauge factors.