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We present some properties of the groups with the infinite non-quasicentral periodic nodal subgroup. Our main results are formulated in Theorem 1, 2 and Theorem 3, 4. 2000 Mathematics Subject Classification: 20F22, 20F25
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Reliability is the important characteristic of systems. Most of the systems consist of more than one component. Moreover, modern systems are very complex and they include a lot of components. Therefore, effective methods have to be developed for analysis of these systems. The techniques that have been already considered for this purpose are the Binary Decision Diagrams and the Logical Differential Calculus. However, these methods have been considered only for the coherent systems. In this paper, their use in the reliability analysis of the noncoherent systems is considered
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Implementation of planar surface photonic crystal (PhC) structures leads to improvement of optical properties of optoelectronic devices. Application of such structures can be attractive for overall and local enhancement of light from patterned areas of the light emitting diode surface and for lightwave-guiding devices. We present techniques useful for PhC patterning and for patterning of different optic structures in surface of new promising material polydimethylsiloxane (PDMS). Paper proposes nanoimprint technology for fabrication of PhC in the surface of thin PDMS membranes for possible application in light emitting diodes. By PDMS patterning and its positioning on the device surface one can achieve original optical properties of optoelectronic devices. We also present new technique for fabrication of surface-relief fiber Bragg grating (SR FBG) based on PDMS waveguide.
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The paper presents examples of incorrectness from the point of view of body and Multibody System (MBS) kinematics. This incorrectness should be kept in mind when modeling Virtual Prototypes (VP) of MBS. During the analysis or synthesis of MBS it is necessary to correctly determine the degree of freedom (DOF) of mechanisms in order to properly design the mechanism. The basic relation for the DOF computation does not include parameters such as special dimensions of links or their mutual configuration and geometric constraints. In many cases, these issues require individual approach, i.e. by analyzing the properties of incorrect MBS to identify the causes of their incorrectness and apply the computation method to the actual mobility. The paper contains samples to illustrate a particular topic.
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Some types of biomass ash have low ash melting temperature which can result in various problems in combustion processes. Ash slags and sinters can avoid heat transfer in heat exchangers, which can also cause corrosion of heat transfer surfaces. One of the ways of burning fuels with low ash melting temperature is to use additives. Ash melting temperature can be determined in a laboratory on the basis of standard STN ISO 540. Meltability of ash is characterized by the physical state of ash occurring during the heating process under well-defined conditions in the furnace. Experimental determination of ash melting temperature is quite expensive. In this work a prediction method of ash melting temperature is described. The mathematical model uses multiple linear regression where input parameters are the known chemical composition of fuel ash and used additive converted to an amount of SiO2, CaO, K2O, MgO and Al2O3. The mathematical model is relatively accurate with real ash melting temperatures and reaches accuracy about of 90 % compared with ash melting temperatures obtained by STN ISO 540 method in a laboratory.
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Nowadays fine-grained, quench and tempered steels are more and more used in design of modern semitrailers constructions. High mechanical properties and durability of this type of steel are its advantage. This paper summarizes the results of research together with the data available by the manufacturer SSAB company. The combination of the special features provided by this material enables construction of lighter semitrailer's components, which would result in a semiauto with a lower weight of its own. This paper presents the results of mechanical properties of Domex 700 MC steel.
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This paper deals with influence on segregation of iron based phases by chrome. Iron is one of the most common impurities that could be found in Al-Si alloys. It is impossible to remove iron from melt by standard operations, but it is possible to eliminate its negative influence by addition of some other elements that affect the segregation of intermetallics in less harmful type. Realization of experiments and results of analysis show new perspective on solubility of iron based phases during melt preparation with higher iron content and influence of chrome as iron corrector of iron based phases. It could be concluded that higher amount of chrome causes the formation of sludge particles.
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The roller bearing is a component which helps to reduce friction on relative rotational or sliding movements of the machine parts. Nowadays, there are many kinds of rolling bearings whose production is constantly improving due to increasing demands on the mechanical properties and durability. An important and necessary step in the production of rolling bearings is the heat treatment. Technological heating process must be created rationally for the required mechanical properties such as hardness, toughness and also dimensional accuracy all with respect to the economic efficiency. Because of the economical demands, simulation software is increasingly beginning to be used in the projection of heat treatment. This simulation software can predict metallurgical and mechanical properties of components after heat treatment, and thus it is easier to select the optimal material design, heat treatment process and it can possibly identify construction deficiencies in the selected part. For simulation of the heat treatment the SWYSWELD software from ESI group was used. As the output value after the simulated heat treatment (quenching) was hardness, composition of microstructure, roundness and residual stresses. These results of the simulation were then compared with the real measured values [1, 2 and 3].
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In this paper the wind speed data from Meteorological observatory Bratislava-Mlynska dolina were statistically analyzed. The data were analyzed based on Weibull and Rayleigh distribution. The distribution parameters were estimated using maximum likelihood method. The both distributions were compared for their performance using the coefficient of determination and the root mean square error. The results indicate that the better performance can be obtained by the Weibull distribution.
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The paper presents the micromechanical modelling of fiber-reinforced composites in order to determine elastic properties of the homogenized material. For this purpose implementation of homogenization theory was required and analyses were performed. The polymer matrix of three-dimensional representative volume element (RVE) of the composites is modelled by the finite element method (FEM). Software for homogenization of material properties uses direct homogenization method which is based on volume average of stresses in the RVE. Homogenization of composite plate is performed by linking MATLAB and ANSYS software. Calculated elastic properties of the homogenized material are given for epoxy matrix reinforced with carbon, fiberglass and kevlar fiber material.
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Process models of super alloys and included finite element modelling simulations are important for optimizing the metal cutting process, allowing industry to make parts faster, better, and at less cost. Innovative measurement methods of the process can be used to improve and verify the accuracy of these models. With these methods, there are many sources of error when using empirical or exact methods such as infrared radiation thermography to measure the temperature distribution of the tool, workpiece, and chip during metal cutting. Furthermore, metal cutting presents unique measurement challenges due to factors such as the high magnification required, high surface speeds and deformations, micro-blackbody effects, changing emissivity, and primary, secondary and tertiary deformations. As part of an ongoing effort to improve our understanding of the uncertainties associated with these measurement methods, multi-measurement sets of experiments were performed. One set explored how accurately the surface temperature of the cutting tool reflects the internal temperature. This was accomplished by measuring the temperature using a thermal camera in the cutting zone. The second set provided high-speed scanning of dynamic processes such as formation of elastic and plastic deformation. For this measurement, a high-speed scanning system was applied, with a macro conversion lens for monitoring micro-structural changes in deformation areas. The next set applied was necessary for recording dynamic processes by the implementation of a piezoelectric measurement device for monitoring cutting forces. The outputs from this multi-measuring system are the basis for verification of theoretical knowledge from this field and elimination of the uncertainties that arise with computational simulation systems.
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This paper presents diagnostics of selected CNC machine tools performed with XL80 laser interferometer with XC80 environmental compensation unit, temperature sensors and XR20-W rotary axis calibrator, working together with XL80 laser. Furthermore, the paper includes the methodology and results of conducted linear and angular error measurements, which supplied data for further analysis. The conclusion section presents results of conducted experiment. Measurement results were presented in figures, charts and tables
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Standard STEP-NC (ISO 14649) presents a new model for data transmission between CAD/CAM systems and CNC machines. This standard eliminates the shortcomings of the standard G-code and provides new possibilities in their management. At the Department of Automation and Production Systems, Faculty of Mechanical Engineering, University of Zilina in the framework of the research activities was solved a project for the implementation options of STEP-NC format by programming of CNC machines. This paper presents the results of research solutions which focused mainly on the analysis of standard STEP-NC, a methodology on the model data according to the standard STEP-NC using the EXPRESS language as well as the creation of software for the transformation of STEP-NC data - „TERMINAL STEP NC“. The software has been verified in the transmission of STEP-NC data to a particular CNC machine control system. Transfer of STEP-NC data applications gives the possibility of verifying the implementation of the new standard in older types of CNC machines.
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The aim of the presented article is to show how to create a mathematical model of the tension mechanism working by a spring motion generation and contacting a rigid body at the end of the motion.
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Biodegradation properties of magnesium and its alloys that can be used for implants are not satisfactory and cause serious problems. These problems can be solved by biodegradable surface coatings. Evaluation of biodegradation process of Mg-3Al-1Zn alloy surfaces after grinding and grinding followed by potential controlled electrodeposition of dicalcium phosphate dihydrate (DCPD) was investigated by electrochemical impedance spectroscopy measurements in this study. The potentiostatic electrodeposition treatment process was performed in water solution of Ca(NO3 )2.4H2 O, NH4 H2 PO4 and H2 O2 . The corrosion process on treated and nontreated samples after various exposure times was evaluated in 0.9% NaCl solution simulating body fluid environment at 37 °C.
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The paper presents the experimental results of various Cu pipes joint corrosion behavior. Joining of copper pipes used for liquid media transport can be made as demountable and fixed joints. The object is to study corrosion resistance of the joints created by soft soldering, hard soldering and fitting. Corrosion properties were investigated by long-term experiment in two identical experimental devices in stagnant and flowing conditions. The experimental environment was water solution of the 3% NaCl, temperature was kept 20° C for 16 hours and 8 hours 80° C per day. In one of the devices for 8 hours the experimental solution was flowing by the input speed 0.27m.s -1. In the second one no flow was applied. Evaluation of the joints corrosion attacks was performed visually, by light and scanning electron microscopy.
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This paper deals with influence of flank wear on decomposition of cutting force in turning roll bearing steel. The decomposition is carried out to evaluate the components of cutting force in the tool-chip as well as tool-workpiece interface. The decomposition enables evaluation of the shear and normal forces in the both interfaces. The results of experiments and the following calculations show that while conditions for chip separation in the tool-chip interface stay nearly untouched due to progressive development of flank wear, mechanical load of machined surface associated with components of cutting forces progressively increases with flank wear. The paper also reports about influence of flank wear on surface integrity expressed in such parameters as residual stresses, surface topography, structure transformation and microhardness.
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The paper deals with use of the meshless method for slope stability analysis. There are many formulations of the meshless methods. The article presents the Local Galerkin Radial Point Interpolation method (LGRPIM) – local weak formulation of the equilibrium equations. The main difference between meshless methods and the conventional finite element method (FEM) is that meshless shape functions are constructed using randomly scattered set of points without any relation between points. The shape function construction is the crucial part of the meshless numerical analysis in the construction of shape functions. The article presents the radial point interpolation method (RPIM) for the shape functions construction. The numerical example of the slope stability was calculated using meshless computer code and compared with FEM results.
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This paper presents the results of estimating the power of Kolmogorov test and its modifications for testing hypothesis about an exponential distribution against the alternative hypothesis (population has a Weibull distribution). The power of test was calculated based on a distribution of empirical cumulative distribution function and limiting distribution, as well as computer-simulation methods. Some important properties and limitations were given that are related to power simulation study of goodness-of-fit tests.
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Headed stud shear connectors are commonly used to transfer longitudinal shear forces across the steel-concrete interface in composite structures. This paper is focused on the experimental and numerical study on the behaviour of this type of connectors. The push-out tests of headed studs, 10 mm in diameter and 50 mm in length, in normal C25/30 concrete with transverse reinforcement were carried out. The experimental study also treated the influence of the connectors spacing, in the longitudinal and transversal directions, and the thickness of the concrete slab on the shear resistance.
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