Hedgehogs are not colour blind

We exhibit a family of $3$-uniform hypergraphs with the property that their $2$-colour Ramsey numbers grow polynomially in the number of vertices, while their $4$-colour Ramsey numbers grow exponentially. This is the first example of a class of hypergraphs whose Ramsey numbers show a strong dependence on the number of colours.Comment: 7 page

Evironmental Tax. Are Vehicle Registers in the EU Prepared?

The market system is unavailable to reflect negative externalities, caused by road motor trafic, in the realized prices. For that purpose, it would be appropriate to implement a general environmental road tax in the European Union member states. The question is whether the national registers of vehicles are prepared for such a change. Whether this is the case at present, may be found out by means of analyses of the available national registers. The next step is synthetic: the data must be subsequently completed on the basis of the knowledge of needs of currently existing systems of road motor vehicles taxation. In the end, the identified results may be supplemented with the known data published by international institutions. The results of the research show that the present systems of road motor vehicles taxation are utterly different and distortive. Only 12 countries of the European Union have registers which were clearly identified as prepared for the application of the environmental tax. Registers of the remaining countries do not contain one or more data that are necessary for the implementation of the environmental tax. For this reason we may assume that regardless of other determinants, environmental road tax shall not be introduced throughout the European Union in the foreseeable future.O

OLAP recommender: supporting navigation in OLAP cubes using association rule mining

The OLAP Recommender tool automates the multidimensional data exploration process and recommends potentially interesting views on the data to the user. It integrates two data analytics methods – OLAP visualisation and data mining, the latter being represented by GUHA association rule mining. Algo-rithms implemented in the tool include automated data discretization, setup of dimensions’ commensurability, automatic design of the data mining task based on the data structure, and mapping between the mined association rules and the corresponding OLAP visualisation. The system was tested with real retail data and with EU structural funds data. The experiments indicate that complemen-tary usage of association rule mining and OLAP analysis identifies relationships in the data with higher success rate than the isolated use of both techniques

Geometrická řešení algebraických úloh MO

summary:Algebraické úlohy zadávané v Matematické olympiádě bývají samy o sobě často na první pohled neintuitivní a jejich autorská řešení matematicky příliš deduktivně dokonalá. Některé z nich ale mají i svou geometrickou interpretaci, u které je poté možné najít řešení pouhým vhledem. V tomto článku jsou uvedena dvě takováto řešení k úlohám, které se objevily v krajských kolech 68. a 64. ročníku Matematické olympiády kategorie A

The Influence of runner system on production of injection molds

This experimental study describes the influence of runner system on rheological properties during the injection molding process. Economic effects on the amount of production are discussed as well. Autodesk Moldflow Synergy 2016 (Moldflow) was used for the study of the injection process. Three suggestions of the runner system, cold runner system, hot runner system and the combination of cold hot runner system have been promoted. These three variants underwent the rheological and economic analysis. As a result, recommendations for the application of the runner system for the required amount of production have been suggested.Ministry of Education, Youth and Sports of the Czech Republic within the National Sustainability Programme [LO1303 (MSMT-7778/2014)]; European Regional Development Fund under the project CEBIA-Tech [CZ.1.05/2.1.00/03.0089]; TBU in Zlin [IGA/FT/2016/010

Field-trial of an all-optical PSK regenerator/multicaster in a 40 Gbit/s, 38 channel DWDM transmission experiment

The performance of future ultra-long haul communication systems exploiting phase-encoded signals is likely to be compromised by noise generated during signal transmission. One potential way to mitigate such noise is to use Phase Sensitive Amplifiers (PSAs) which have been demonstrated to help remove phase as well as amplitude noise from phase-encoded signals. Recently, we showed that a PSA-based signal regenerator based on degenerate four-wave mixing can be implemented in a network-compatible manner in which only the (noisy) signal is present at the device input (black-box operation). The developed regenerator was also able to perform simultaneous wavelength conversion and multicasting, details/analysis of which are presented herein. However, this scheme was tested only with artificial noise generated in the laboratory and with the regenerator placed in front of the receiver, rather than in-line where even greater performance benefits are to be expected. Here, we address both theoretically and experimentally the important issue of how such a regenerator, operating for convenience in a multicasting mode, performs as an in-line device in an installed transmission fiber link. We also investigate the dispersion tolerance of the approach

Polymer fluidity influenced by type and amount of filler

Delivery of polymer melts into the mold cavity is the most important stage of the injection molding process. This paper shows the influence of cavity surface roughness and technological parameters on the flow length of polymers into mold cavity. Application of the measurement results may have significant influence on the production of shaping parts of the injection molds especially in changing the so far used processes and substituting them by less costly production processes which might increase the competitiveness of the tool producers and shorten the time between product plan and its implementation. This research focused into the influence of technological parameters on filling of the injection mold cavity and the flow length respectively.Ministry of Education, Youth and Sports of the Czech Republic within the National Sustainability Programme [LO1303 (MSMT-7778/2014)]; European Regional Development Fund under the project CEBIA-Tech [CZ.1.05/2.1.00/03.0089]; TBU in Zlin [IGA/FT/2016/010

Influence of length of glass fibers in recycled polypropylene on tensile properties

The purpose of this article is to show the influence of grinded glass fibers in polymer material. Tested samples were processed by injection molding. Waste from this production was subsequently ground and a mixture was obtained with different size of crushed material. These particles contains glass fibers of similar length as the specific size of particle. Thus very small particles contain very short fibers. Investigation was carried out by testing tensile properties on material polypropylene with 30% glass fibers. Testing was conducted at ambient temperatures. The effect of reprocessing of material is mainly represented by fiber shortening. As a result, considerable reduction of tensile properties can be observed. The reduction is most evident in the modules of elasticity and ultimate tensile strength.TBU in Zlin [IGA/FT/2016/010]; Ministry of Education, Youth and Sports of the Czech Republic within the National Sustainability Programme [LO1303 (MSMT-7778/2014)]; European Regional Development Fund under the project CEBIA-Tech [CZ.1.05/2.1.00/03.0089

Mechanical properties of injection molded and compression molded samples from nature-butadiene rubber

The aim of this paper is to show what extent there is an impact on the mechanical properties (tensile strength and tear strength) of a standardized testing sample made of rubber compound based on nature rubber and butadiene rubber produced by injection molding in comparison with a sample produced by classic preparation (cutting out a compression molded plate) according to the standard ISO 23529. For realization of this study it was necessary to design and produce an injection mold for all types testing samples. Subsequently, mechanical properties such as the tensile stress-strain and tear strenght of compression molded samples and injection molded samples were studied, compared and discussed.TBU in Zlin [IGA/FT/2016/010]; Ministry of Education, Youth and Sports of the Czech Republic within the National Sustainability Programme [LO1303 (MSMT-7778/2014)]; European Regional Development Fund under the project CEBIA-Tech [CZ.1.05/2.1.00/03.0089