A New Approach for Trend Assessment of Annual Streamflows: a Case Study of Hydropower Plants in Serbia

The authors propose a new approach for trend assessment that takes into account long-term periodicity of annual flows. In particular, analysis is performed of annual flows recorded at the locations of 30 operating and designed hydropower plants (HPPs) in Serbia, in order to assess the current and future water availability for hydropower generation. The composite annual trend is determined by sliding a fixed time window of 30 years along the observed time series with a one-year time step. Such a linear moving window (LMW) approach enables the identification of the flow trend as a median of all values for each time step. Significant trend harmonics are determined using discrete spectral analysis. The results show an alternation of upward and downward trend phases of different durations, namely: 67–87, 33–43 and 21–29 years. On the other hand, the results of the Mann-Kendall test indicate a monotonic downward trend at the studied sites in the Drina River Basin, while statistically insignificant trends are noted at other river basins. The Mann-Kendall test with the Theil-Sen estimator also implies a downward and statistically insignificant flow trend after the observed period, whereas the LMW approach indicates a probable trend increase at all the examined sites. The proposed approach can be used to predict annual flows in order to establish long-term water management plans at hydropower plants.     

Tesla’s Fountain – Modeling and simulation in ceramics technology

In this paper, we present Tesla’s Fountain in ceramics technology reconstruction from basic 3D model, simulation of the engine, light and fluids till the real materialization. As the one of the most important model purposes, we enrich this solution by additional multicolor lights. All of this elements are designed based on Tesla’s original patent no. 1,113,716, US patent office, granted Oct,13. In this model we applied ceramics technology based on ceramic materials casting and sintering. At the time when the patent was granted, the metal materials science and technologies were more advanced than the ceramics technology and applications. We performed all materials characteristics analyses and preparation steps based on the one author’s patent no. 46121, Serbia patent office, granted 21.12.1991. This is one original two patents solution with complete new over-bridging by the state-of-the-art computer modeling and simulation technology.     

Optimization of a nanoparticle ball milling process parameters using the response surface method

Nanocrystalline TiO₂-CeO₂ powders were synthesized from their TiO₂ and CeO₂ oxides using mechanical ball milling process. The response surface method is applied to identify optimal parameters for the synthesis of TiO₂-CeO₂ photocatalyst. Analysis of variance and main effect plot are used to determine the significant parameters and set the optimal level for each parameter. Regression analysis showed good agreement of experimental data with the second-order polynomial model with a coefficients of determination: R²?=?0.991, R²_Adj.?=?0.940 and R²_Pred.?=?0.983. Under optimal experimental conditions of TiO₂:CeO₂ weight percentage ratio 71:29, milling speed 200?rpm, and milling time 115?min the highest photodegradation efficiency was achieved. On the basis of the above statistical analysis, it was found that the band gap energy of TiO₂-CeO₂ nanoparticles decreases with the increase of the milling speed and milling time with constant TiO₂:CeO₂ weight percentage ratio. Obtained results suggest that mechanical ball milling process is a rapid, efficient and low energy consumption method to synthesize TiO₂-CeO₂ photocatalyst.     

The economic effects of energetic exploitation of straw in Vojvodina

The autonomous province of Vojvodina is an autonomous province in the Republic of Serbia. It is located in the northern part of the country, in the Pannonia plain. Vojvodina is an energy-deficient province.Assessment of the effects of energetic use wheat straw is performed for certain types of systems for storing straw and straw stored specifically in the form of small square bales, and especially for the cylinder-shaped straw bales. The method of evaluation of economic effects is based on the total cost of collecting, transportation, handling and storing, with corrections for the difference in the cost of the energy conversion and combustion.With comparison of the costs of energy production from baled straw to the costs of energy production from hard coal, it was found that the energy obtained from the straw from own farm is cheaper than energy from hard coal by 28%, in the case of the using small square bales and by 34% in the case of the using cylinder-shaped bales. Through sensitivity analysis it was concluded that the two systems of collecting straw, economically, are relatively resistant to changes in prices of the most important inputs. However, there is a relatively high sensitivity to changes in performances of machines with a larger percentage increase of costs for the system with cylinder-shaped bales. However, this system is generally more resistant to changes of influencing factors due to lower basic costs per ton of the pretreated straw. Differential costs analysis, i.e., the development of differential calculations, shows that the energy from straw in the form of small square bales is cheaper than the energy from hard coal by 51%, while the energy from the straw in the form cylinder-shaped bales is cheaper by 60%.     

Multi-fractal morphology of un-aged and aged SBS polymer-modified bitumen

Polymer-modified bitumen (PmBs) has been characterised by fluorescence microscopy, conventional performance tests and by the rheological measurements, before and after the Rolling Thin Film Oven Test (RTFOT), and by multi-fractal analysis. The addition of 2–7 wt-% of linear styrene-butadiene-styrene block copolymer (SBS-L) or radial block copolymer (SBS-R) increased viscosity, softening point and complex modulus of PmBs. Hardening of PmBs occurred and the elastic response decreased after RTFOT aging. SBS-L PmBs are more susceptible to RTFOT aging. Digital fluorescence micrographs of sections of PmBs qualitatively exhibit different morphological structures which can be quantitatively probed by multi-fractal analysis: differences are reflected in the f (α) spectrum. The PmBs which appear less multi-fractal have the best rheological properties. In another approach, the focal fractal dimensions’ distributions for the SBS-modified bitumen have peak around 2.35 (which corresponds to the bitumen-rich phase) and around 2.7 (which corresponds to the noncontinuous SBS-rich phase).     

General approach to reliable characterization of thin metal films

Optical constants of thin metal films are strongly dependent on deposition conditions, growth mode, and thickness. We propose a universal characterization approach that allows reliable determination of thin metal film optical constants as functions of wavelength and thickness. We apply this approach to determination of refractive index dispersion of silver island films embedded between silica layers.