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Search Results: 1 - 10 of 7341 matches for " Ve?ko-Pirtov?ek "
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Wear Beahaviour of Nitrided Microstructures of AlSl H13 Dies for Hot Extrusion of Aluminium
Kugler, G.,Turk, R.,Veko-Pirtovek, T.,Ter?elj, M.
Metalurgija , 2006,
Abstract: Nitriding of bearing surfaces on dies (tools, AISI H13) for hot extrusion of aluminium is technologically a very sensitive process with regard to achieving a constant quality of the nitrided layers. This study was based on the analysis of microstructure on dies with intentionally prepared deep and narrow gaps which were nitrided by various manufacturers of equipment for gas and ionic nitriding. The manufacturers chose their own nitriding parameters in order to achieve an optimal wear resistant microstructure. The microstructures obtained showed differences with regard to the presence or absence of a compound layer (white layer), its thickness and its e/g' phase ratio (XRD), nitriding depth and microhardness profile. The measured nitriding depths and the maximum microhardness values on nitrided surface layers were quite similar on dies of the same manufacturer, while for different manufacturers these values differed. Differences with regards to compound layer characteristics were also found on the same die. The die samples with these various nitrided microstructures were then laboratory tested for wear resistance using equipment that provides simulation of the tribological conditions during hot extrusion of aluminium. The wear testing results show differences in behaviour of the nitrided samples. The differences in the actual structures, microstructures, hardness, etc. explain the high level of scattering in die life in actual industrial applications.
Hot forming of AISI A2 tool steel
T. Veko Pirtovek,I. Peru?,G. Kugler,R. Turk
Metalurgija , 2008,
Abstract: For further increase of economy of production of AISI A2 tool steel a study of possibility of expanding the hot working range and better prediction of flow stress has been carried out. By employing hot compression tests it was proved, that initial microstructures have influence on the lower limit and chemical composition on upper limit of hot working range. A CAE Neural Networks was applied to predict the flow stresses for intermediate values of strain rates and temperatures. For optimization purposes the activation energies and constants of the hyperbolic sine function for two temperatures ranges (850-1000°C and 1000-1150°C) were calculated.
Construction of Three Quadrature Formulas of Eighth Order and Their Application for Approximating Series  [PDF]
Bogus?aw Bo?ek, Bogus?aw Bo?ek, Wies?aw Solak, Zbigniew Szyde?ko
Applied Mathematics (AM) , 2015, DOI: 10.4236/am.2015.66095
Abstract: In this paper, three types of three-parameters families of quadrature formulas for the Riemann’s integral on an interval of the real line \"\" are carefully studied. This research is a continuation of the results in the [1]-[3]. All these quadrature formulas are not based on the integration of an interpolant as so as the Gregory rule, a well-known example in numerical quadrature of a trapezoidal rule with endpoint corrections of a given order (see [4]). In some natural restrictions on the parameters we construct the only one quadrature formula of the eight order which belongs to the first, second and third family. For functions whose 8th derivative is either always positive or always negative, we use these quadrature formulas to get good two-sided bound on \"\". Additionally, we apply these quadratures to obtain the approximate sum of slowly convergent series \"\", where \"\".
The Late Miocene Guacimal Pluton in the Cordillera de Tilarán, Costa Rica: its nature, age and petrogenesis
?á?ek V,Janou?ek V,Ulloa A,Ko?ler J
Journal of Geosciences , 2011, DOI: 10.3190/jgeosci.087
Abstract: The Guacimal Pluton is situated in the Cordillera de Tilarán in the northwestern Costa Rica. It forms an oval-shaped body strongly elongated in the NW—SE direction. Its dimensions are 15 × 4—6 km with an exposed surface of 60—70 km2. The pluton intruded basic volcanic rocks of the Aguacate Group (Miocene—Pliocene) and is surrounded by a wide thermal aureole of calc-silicate metasomatic rocks. The pluton is mainly formed by monzogranites to granodiorites, which strongly prevail over more basic types forming scarce and relatively thin dykes and enclaves. The dominant magmatic minerals of this felsic suite are quartz, plagioclase, and K-feldspar with subordinate Mg-rich biotite, amphibole I, and magnetite. Orthopyroxene, Mn-rich ilmenite, Al-poor titanite, rutile, apatite, zircon, thorite, and chalcopyrite are accessory. Secondary minerals, which occur as fillings of miarolitic cavities and interstices, are quartz II, K-feldspar II, epidote, chlorite, actinolite, ilmenite II and Al-rich titanite II. The much less frequent mafic suite (mainly quartz diorite to quartz monzodiorite/monzogabbro) is composed of plagioclase, pargasite, actinolite, K-feldspar, quartz and magnetite, with accessory amounts of opaque minerals, epidote, chlorite, and titanite. The pluton was emplaced at a depth of c. 3 km, crystallized at temperature of c. 760—800 °C under a relatively high oxygen fugacity (1.6—2.1 log units above the NNO buffer). Increased activities of volatiles (H2O, F) upon cooling are indicated by the presence of highly aluminous, F-rich titanite and other hydrous silicates in miarolitic cavities. The prevailing, felsic rocks of the Guacimal Pluton are high-K calc-alkaline, whereas the mafic suite is nearly exclusively medium-K calc-alkaline in nature. Laser ablation ICP-MS dating of zircons from two granite samples yielded statistically identical U—Pb ages of 6.3 ± 0.5 and 6.0 ± 0.4 Ma, respectively. The Sr—Nd isotopic compositions are rather primitive (87Sr/86Sr6 = 0.70380—0.70413, ε6Nd +7.3 to +7.9). Narrow range of these values effectively rules out open-system processes such as magma mixing or assimilation of isotopically contrasting upper continental crust. Instead, the felsic suite is interpreted as either having crystallized from a highly fractionated melt extracted from a plagioclase—amphibole-dominated crystal mush in a putative deep crustal reservoir or a product of partial melting of older arc-related rocks, such as intermediate lavas or volcaniclastics, immature psammitic sediments rich in volcanic material etc. The observed variation in the fels
Medosebni odnosi in vsebina dela kot dejavnika stresa pri srednjem managementu = Interpersonal Relationships and Work Content as Stress Factors among Middle Management
Polona Ko?uh,Ana Arzen?ek
Management , 2011,
Abstract: In the modern society, where importance is placed on progress, newtechnologies and economic trends, there is a lack of awareness of thesignificance of good interpersonal relations and organizational culturewithin a company. They both contribute to the better functioningof employees as well as the entire organization. The purpose of thisstudy was to determine any possible differences between the stressorslinked to the relationships within an organization and those linked tothe work of middle management. The study included 58 middle managersworking in commercial activity in the Ljubljana region. The resultshave indicated that the amount of stressors related to the relationships,and stressors related to the managers’ work, that affect themiddle managers participating in the survey is on average the same.The results have therefore shown no statistically significant differencebetween the two forms of the studied stress factors.
Scattering model for quantum random walk on the hypercube
Jozef Ko?ík,Vladimír Bu?ek
Physics , 2004, DOI: 10.1103/PhysRevA.71.012306
Abstract: We elaborate on a model of quantum random walk proposed by Hillery et. al., and Jeong et. al., which uses the multiports for quantum "coin tossing". The dynamics of this model is analyzed for the case when the multiports are arranged on the hypercube. If the hypercube is attached to semi-infinite lines, then it can act as a scattering potential, which can be reduced to a quantum walk on the line with non-unitary evolution. We also show how this model can be implemented using simple quantum gates.
On the Problem of Formulating Principles in Nonequilibrium Thermodynamics
Pa?ko ?upanovi?,Domagoj Kui?,Davor Jureti?,Andrej Dobovi?ek
Entropy , 2010, DOI: 10.3390/e12040926
Abstract: In this work, we consider the choice of a system suitable for the formulation of principles in nonequilibrium thermodynamics. It is argued that an isolated system is a much better candidate than a system in contact with a bath. In other words, relaxation processes rather than stationary processes are more appropriate for the formulation of principles in nonequilibrium thermodynamics. Arguing that slow varying relaxation can be described with quasi-stationary process, it is shown for two special cases, linear nonequilibrium thermodynamics and linearized Boltzmann equation, that solutions of these problems are in accordance with the maximum entropy production principle.
Implementation of Safety Assurance System in Food Production in Poland
Joanna Trafia ek, Danuta Ko o yn-Krajewska
Polish Journal of Food and Nutrition Sciences , 2011, DOI: 10.2478/v10222-011-0012-x
Abstract: This study has examined the impact of Poland's accession to the European Union in 2004 and that of implementation of EU legal regulations in food legislation on the decision of the HACCP being implemented by middle and small size food production companies in Poland. Problems accompanying the system implementation and advantages ensuing it were reviewed. The biggest problems included the necessity of the processing plant incurring expenses and being revamped, incomprehension of the HACCP system idea by employees, and the quantity/quality barrier. The greatest advantage is an increase in employees' responsibility for production hygiene, improved safety of manufactured products, an increased prestige of the company and its products, a growth in employees' involvement in their work and enhancement of their qualifications as well as improved safety of manufactured products and maintenance of the market position.
On some quadrature rules with Gregory end corrections
Bogus?aw Bo?ek,Wies?aw Solak,Zbigniew Szyde?ko
Opuscula Mathematica , 2009,
Abstract: How can one compute the sum of an infinite series $s := a_1 + a_2 + \ldots$? If the series converges fast, i.e., if the term an tends to 0 fast, then we can use the known bounds on this convergence to estimate the desired sum by a finite sum $a_1 + a_2 + \ldots + a_n$. However, the series often converges slowly. This is the case, e.g., for the series $a_n = n^{-t}$ that defines the Riemann zeta-function. In such cases, to compute $s$ with a reasonable accuracy, we need unrealistically large values $n$, and thus, a large amount of computation. Usually, the $n$-th term of the series can be obtained by applying a smooth function $f(x)$ to the value $n: a_n = f(n)$. In such situations, we can get more accurate estimates if instead of using the upper bounds on the remainder infinite sum $R = f(n + 1) + f(n + 2) + \ldots$, we approximate this remainder by the corresponding integral $I$ of $f(x)$ (from $x = n + 1$ to infinity), and find good bounds on the difference $I - R$. First, we derive sixth order quadrature formulas for functions whose 6th derivative is either always positive or always negative and then we use these quadrature formulas to get good bounds on $I - R$, and thus good approximations for the sum $s$ of the infinite series. Several examples (including the Riemann zeta-function) show the efficiency of this new method. This paper continues the results from [3] and [2].
A note on a family of quadrature formulas and some applications
Bogus?aw Bo?ek,Wies?aw Solak,Zbigniew Szyde?ko
Opuscula Mathematica , 2008,
Abstract: In this paper a construction of a one-parameter family of quadrature formulas is presented. This family contains the classical quadrature formulas: trapezoidal rule, midpoint rule and two-point Gauss rule. One can prove that for any continuous function there exists a parameter for which the value of quadrature formula is equal to the integral. Some applications of this family to the construction of cubature formulas, numerical solution of ordinary differential equations and integral equations are presented.
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