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Search Results: 1 - 10 of 5210 matches for " Vojtěch Havel "
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LTL Model Checking of Parametric Timed Automata
Peter Bezděk,Nikola Bene?,Vojtěch Havel,Ji?í Barnat,Ivana ?erná
Computer Science , 2014,
Abstract: The parameter synthesis problem for timed automata is undecidable in general even for very simple reachability properties. In this paper we introduce restrictions on parameter valuations under which the parameter synthesis problem is decidable for LTL properties. The proposed problem could be solved using an explicit enumeration of all possible parameter valuations. However, we introduce a symbolic zone-based method for synthesising bounded integer parameters of parametric timed automata with an LTL specification. Our method extends the ideas of the standard automata-based approach to LTL model checking of timed automata. Our solution employs constrained parametric difference bound matrices and a suitable notion of extrapolation.
Monitoring of X-Ray Sources in the Optical Spectral Region
Vojtěch ?imon
Advances in Astronomy , 2010, DOI: 10.1155/2010/382936
Abstract: We review current results and perspectives of the photometric monitoring of the optical counterparts of X-ray sources of various kinds (binary X-ray sources (cataclysmic variables and low-mass X-ray binaries, supersoft X-ray sources, microquasars), gamma-ray bursts). We discuss the problems of the monitoring of the individual kinds of objects in the optical and X-ray passbands. We show the importance of multifilter monitoring to obtain a deeper understanding of the physical processes and to resolve between the individual emission mechanisms. We also show that there are brief, unique, and little understood phenomena which are very promising targets for the optical monitoring, for example, flares in intermediate polars. 1. Introduction This review deals with the observations of the optical counterparts of sources of high-energy emission. Since the research field of the high-energy sources is already very broad, we have to limit this topic. We will concentrate on the systems which contain a compact object with the mass comparable with the stars, that is, excluding supermassive black holes present in active galactic nuclei. Furthermore, we will concentrate on the systems and events in which the optical emission radiated by the accreting matter dominates. Our review is focused on binary X-ray sources (cataclysmic variables (CVs), low-mass X-ray binaries (LMXBs), supersoft X-ray sources, microquasars), gamma-ray bursts (GRBs). These objects are very important laboratories for the study of the physical processes occurring in extreme conditions. However, their activity on long timescales of months, years, and even decades remains little studied, although it is very important for our understanding of the relevant physics. A search for and analysis of rare dramatic variations of activity like outbursts of various kinds which reflect huge changes of the physical processes are particularly exciting. Study of the long-term activity requires monitoring of the individual objects (if they are already identified), or even monitoring of the large fields of the sky to search for the events like optical afterglows of GRBs. 2. Binary X-Ray Sources CVs and LMXBs are binary systems in the phase of mass exchange (e.g., [1, 2]). They contain a compact object (white dwarf in CVs, neutron star, or black hole in LMXBs) which accretes matter from its Roche lobe-filling companion (the so-Called donor). The donor is usually a late type main-sequence star, but also rare cases where it is a subgiant or a white dwarf are known (the type of the donor depends on the orbital period ranging
Vysledky druhého kola senátních voleb 1996–2008: kdo, proti komu, odkud a jak
Vojtěch Navrátil
St?edoevropské Politické Studie , 2010,
Abstract: The Results of the Second Round of the Senatorial Elections 1996–2008: Who, against Whom, from Where and How. The article is concerned with a descriptive analysis of the second round of the senatorial elections in the Czech Republic from 1996 in three various aspects. Attention is devoted to the success of candidates who passed to the second round as winners in the first round, and the success of candidates according to the relation to their election district. There has been a total of 241 second-round contests since 1996. An absolute majority system with run-off has been used in these elections.
DISCUSSING THE SUNK COST FALLACY: TOWARDS A HIERARCHICAL CONCEPT OF RATIONALITY IN MANAGERIAL DECISION-MAKING
VOJTěCH OPLE?TIL
Ad Alta : Journal of Interdisciplinary Research , 2011,
Abstract: An assertion widespread in economics, psychology, and managementmaintains that giving weight to sunk costs is irrational. However, there is a growingdiscussion which points to some aspects of such behaviour which may indicate thatunder certain circumstances giving weight to sunk costs is not irrational. In this articleI suggest that the above mentioned discussion has wider implications for practical andtheoretical management. When dealing with the rationality of management actions,assessment of their rationality is always connected with their value, organizational andcognitive context. I propose a concept of hierarchical rationality which respects theambiguity of context and various goals and values both individual and organizationmay follow. Such a concept offers for management some practical impulses.
Challenges for research and development of new aluminum alloys
D. Vojtch
Metalurgija , 2010,
Abstract: Modern trends in research and development of new aluminum alloys are characterized in the present work. Although conventional wrought and casting Al-based alloys show good specific strength, as compared to steels or Ti-based alloys, there is still a potential for significant improvement of their performance. It consists in application of new alloying elements, mainly transition metals, and uncommon processing routes, for example powder metallurgy. By this way, qualitatively new materials with ultra high strength and excellent thermal stability can be developed. However, there are many questions to be answered before new alloys can be competitive to conventional Al-based materials.
The Problems of the Identical Product Name on the EU Common Agrarian Market
Vojtěch TAMá?
Annals of Dun?rea de Jos University. Fascicle I : Economics and Applied Informatics , 2008,
Abstract: The paper deals with the current problem of agrarian sector withinfluence mainly to food producers. It deals with their impact on changes ofagricultural producer’s position in a framework of food production systems.Concretely paper deals with the problems of risk related to milk products pricingdistortion due to possibility of substitution milk fat behalf vegetable fat. Togetherwith formation of such a risk, food producers are dealing with the other problem,which is using of the similar product name on the common market of EU. Problemis currently related to using the term “spread butter“, which is denoted as deceivebecause of harming a butter producers. There is an argument that by the influenceof currently used term might be those two products consider as a perfect substitutes,between which arise an elicitation of the cross substitution effect. On the Europeanenlarged market of the food could to several situations occur, particularly if there isan offer of the products of the similar, or even the same product name. This is veryoften visible on the EU common market, this naturally cause problems especially ifthe composition of the product and the production technology are completelydifferent. The solution of this problem is linked to the question of the economicalsubstitution, which is usually related to completely different products. This bringsabout damage to food producers on the first side, and also a deception of consumeron the second side. The example of such as situation is currently visible on theEuropean dairy market, concretely in the case of dairy products. In this article willbe explained the situation linked to problem of the Czech producers of “Spreadbutter”, which is a traditional Czech product and the producers of the “Traditionalbutter”.European Commission ruled in producers of “Traditional Favour” favour,which means that it will be no longer possible to sell products, with lower than 39%of milk fat, under the product name “butter”. From the economic theory is wellknown [3] GRAVELLE, that substitution effect describes the effects of changes inrelative prices on consumption. According to the substitution effect, an increase inprice of one good causes a buyer to buy more of the other good, since the first goodhas become relatively expensive, and vice versa. The buyer substitutes consumptionof the second good for consumption of the first. Therefore even a small pricechange could cause a significant change of the optimal combination in the terms ofthe quantity of the both commodities (in our case spread butter and traditionalbutter.
Crystallography and Magnetic Phenomena
Vojtěch Kopsky
Symmetry , 2015, DOI: 10.3390/sym7010125
Abstract: This essay describes the development of groups used for the specification of symmetries from ordinary and magnetic point groups to Fedorov and magnetic space groups, as well as other varieties of groups useful in the study of symmetric objects. In particular, we consider the problem of some incorrectness in Vol. A of the International Tables for Crystallography. Some results of tensor calculus are presented in connection with magnetoelectric phenomena, where we demonstrate the use of Ascher’s trinities and Opechowski’s magic relations and their connection. Specific tensor decomposition calculations on the grounds of Clebsch Gordan products are illustrated.
Density not realizable as the Jacobian determinant of a bilipschitz map
Vojtěch Kalu?a
Mathematics , 2014,
Abstract: Are every two separated nets in the plane bilipschitz equivalent? In the late 1990s, Burago and Kleiner and, independently, McMullen resolved this beautiful question negatively. Both solutions are based on a construction of a density function that is not realizable as the Jacobian determinant of a bilipschitz map. McMullen's construction is simpler than the Burago-Kleiner one, and we provide a full proof of its nonrealizability, which has not been available in the literature.
Subset Synchronization and Careful Synchronization of Binary Finite Automata
Vojtěch Vorel
Computer Science , 2014,
Abstract: We present a strongly exponential lower bound that applies both to the subset synchronization threshold for binary deterministic automata and to the careful synchronization threshold for binary partial automata. In the later form, the result finishes the research initiated by Martyugin (2013). Moreover, we show that both the thresholds remain strongly exponential even if restricted to strongly connected binary automata. In addition, we apply our methods to computational complexity. Existence of a subset reset word is known to be PSPACE-complete; we show that this holds even under the restriction to strongly connected binary automata. The results apply also to the corresponding thresholds in two more general settings: D1- and D3-directable nondeterministic automata and composition sequences over finite domains.
Two Results on Discontinuous Input Processing
Vojtěch Vorel
Computer Science , 2015,
Abstract: First, we show that universality and other properties of general jumping finite automata are undecidable, which answers a question asked by Meduna and Zemek in 2012. Second, we close the study raised by \v{C}erno and Mr\'{a}z in 2010 by proving that clearing restarting automata using contexts of size two can accept binary non-context-free languages.
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