Results 1 - 10 of 76
Results 1 - 10 of 76. Search took: 0.019 seconds
|Sort by: date | relevance|
[en] The grey iron casting manufacture is an industrial process extendly used today. Therefore, the study of the solidification features obtained from this iron and the factors that have influence on such transition becomes a powerful tool in order to support the technological development of this type of material. In the present work, three inoculated alloys with different chemical compositions (hypo eutectic, eutectic and hyper eutectic) have been selected so as to comparatively analyse the structural characteristics of the irons during the liquid-solid transformation. The behaviour of the samples has been controlled recording the cooling curves and then they have been quenched in order to study the structural characteristics at different stages of the solidification. The selected alloys show different solidification features as a function of the chemical composition and the corresponding nucleation potential. The obtained results have been discussed in terms of a comparative analysis, establishing a solidification model that explains the industrial behaviour of the alloys. (Author)
[en] The aim of the study is the research of early aand delayedeffects of ionizing radiation on a sublethal dose of 3 Grey in cardiomyocytes. On the background of the hydrolysis of cell membrane phospholipids and activation of their peroxidation increased calcium load in the myocardium. The obtained data suggest a correlation relationship of antioxidant, phosphoinositide and prostaglandin regulatory systems
[en] The energy content of (exact) electromagnetic and gravitational plane waves is studied in terms of super-energy tensors (the Bel, Bel–Robinson and the—less familiar—Chevreton tensors) and natural observers. Starting from the case of single waves, the more interesting situation of colliding waves is then discussed, where the nonlinearities of the Einstein’s theory play an important role. The causality properties of the super-momentum four vectors associated with each of these tensors are also investigated when passing from the single-wave regions to the interaction region. (paper)
[en] Highlights: • Storage of forest wood chips and unchipped wood was examined in extensive field trials. • Trials were conducted during winter and summer and with and without rain cover. • Influencing factors on drying and dry matter loss were detected using factorial ANOVA. • Drying can compensate dry matter loss regarding energy content under certain conditions. • Storage before chipping can increase quality of wood chips (fine and ash content). - Abstract: The storage of wood chips is important for the biomass supply chain as it compensates for temporal differences in production and consumption. Typical storage-related problems are dry matter and energy losses due to microbial activity. In extensive field trials, we investigated the storage of spruce wood chips from forest residues (FRC) and from energy roundwood (ERC) with and without rain protection under Central European conditions. Additionally, we examined the storage of unchipped piles. The results indicate that the investigated factors, i. e. storage duration, season, assortment and rain protection, have a statistically significant influence on moisture content and dry matter loss of wood chips. During five months of storage, the highest decline in moisture content was 22.6 %-points, the highest dry matter loss 11.1 %. In winter, energy losses reached up to 11.3 %. In summer, energy contents did not change or even increased slightly (max. 4.7 %). Pile temperature and dry matter losses were significantly positively correlated in FRC. Formation of different layers within the piles could be detected. Storage performance was better in unchipped than in chipped energy roundwood. Storage of unchipped forest residues was not beneficial concerning energy content, but fuel quality increased due to reduced ash and fine particle content. Clear best practice recommendations could be drawn regarding wood chip storage under Central European conditions. During winter, FRC should be stored with rain protection or as short as possible while during a dry and warm summer, wood chips can be stored with only few restrictions.
[en] We study the energy content of colliding plane waves using approximate Noether symmetries. For this purpose, we use the approximate Lie symmetry method for Lagrangians for differential equations. We formulate the first-order perturbed Lagrangian for colliding plane electromagnetic and gravitational waves. In both cases, we show that no nontrivial first-order approximate symmetry generator exists. (author)
[en] Highlights: • Simulation allows predicting the time of maximum energy content and the net present value of a forest fuel pile. • Optimizing the combustion sequence can improve the gained net present value of delivered biomass by 2.0%–6.4%. • The presented simulation and optimization method uses easily available input and is computationally efficient. - Abstract: We constructed a computation scheme that combines GIS, simulation and optimization techniques for assessing the moisture change, dry matter loss, transportation costs and net present value of solid forest fuel piles. This scheme was applied to predict the value of a stock composed of multiple piles, and to find the optimal feedstock allocation strategy, i.e. the selection of piles and the combustion time so that the total energy yield or the economic value of the energy production is maximized. According to the simulation, single Norway spruce energy wood piles reached their maximum energy content during July–August in boreal conditions in Finland. If a pile was created between January–September, the maximum energy content occurred in the same year, whereas for piles created between October–December, the maximum occurs in the summer of the following year. In the optimized combustion sequence, the piles generated in early Year 1 were combusted first. The main outcome of the study was that the simulation-optimization scheme can increase the gained net present value of the feedstock by 2.0%–6.4%, and the benefit increases with increasing heterogeneity of the feedstock. Forest fuel supplier can get considerable savings by applying the presented system to decide the combustion sequence of the existing feedstock. From practical point of view this is remarkable because the savings can be achieved without any investments only by arranging the transportation sequence. The presented computation system uses easily available input, can be modified to different condition, and can be run with standard IT-resources.
[en] We present a simple (microscopic) model in which bulk viscosity plays a role in explaining the present acceleration of the universe. The effect of bulk viscosity on the Friedmann equations is to turn the pressure into an 'effective' pressure containing the bulk viscosity. For a sufficiently large bulk viscosity, the effective pressure becomes negative and could mimic a dark energy equation of state. Our microscopic model includes self-interacting spin-zero particles (for which the bulk viscosity is known) that are added to the usual energy content of the universe. We study both background equations and linear perturbations in this model. We show that a dark energy behavior is obtained for reasonable values of the two parameters of the model (i.e. the mass and coupling of the spin-zero particles) and that linear perturbations are well-behaved. There is no apparent fine tuning involved. We also discuss the conditions under which hydrodynamics holds, in particular that the spin-zero particles must be in local equilibrium today for viscous effects to be important
[en] In order to help assessment of enhanced geothermal energy potential in Canada, we constructed a new series of heatflow and depth–temperature distribution maps (down to 10 km). We focus on high-temperature resources (>150 °C) capable of electrical production. Maps presented show large temperature variability, related mainly to heat flow patterns. The highest temperatures occur in western and northern Canada. Here temperatures greater than 150 °C, required for enhanced geothermal systems (EGS), can be reached at reasonable drilling depths of <5 km. Heat flow, by itself however, is not a sufficient tool to predict areas of high energy content. A combination of thick low thermal conductivity sedimentary blankets and moderate to high heat flow areas can generate targets that are as favorable as regions with high conductivity and high heat flow. Some moderate heat flow areas in the deeper parts of the Western Canada Sedimentary Basin have heat content comparable to high heat flow zones of the the Canadian Cordillera. The magnitude of in-place thermal energy available for future heat 'mining/farming' was esitmated throughout Canada by calculating heat released through cooling a defined rock volume through a fixed temperature change. These estimates show the first-order appoximation of available geothermal heat content. The fraction of true heat energy available will be as low as 0.02 of these values. However, even this more limited energy production could be large enough to be a considerable future renewable energy resource for Canada
[en] We show that the galactic dark matter halo, considered composed of an axionlike particles Bose-Einstein condensate  trapped by a self-graviting potential , may be stable in the Thomas-Fermi approximation since appropriate choices for the dark matter particle mass and scattering length are made. The demonstration is performed by means of the calculation of the potential, kinetic and self-interaction energy terms of a galactic halo described by a Boehmer-Harko density profile. We discuss the validity of the Thomas-Fermi approximation for the halo system, and show that the kinetic energy contribution is indeed negligible
[en] In this work, CR-39 (a commercial polymer) was used as an alpha spectrometer, based on the relationship between the diameter and the trace gray scale with the energy of the incident alpha particle. A rock from Presidente Prudente region (SP, Brazil), containing a fossil, was analysed and a comparison of the activities in the areas with and without the fossil sample have been compared