Dušan Rakić

Isotherms for the adsorption of Cu(II) onto lignin: Comparison of linear and non-linear methods

Equilibrium studies were carried out for the adsorption of Cu(II) onto Kraft lignin as an adsorbent. The experimental data were fitted to the Freundlich, Langmuir and Redlich-Peterson isotherms by linear and non-linear method. Comparison of linear and non-linear regression method was given in selecting the optimum isotherm for the experimental data. The coefficient of correlation r2 and Chi-square test χ2 was used to select the best linear theoretical isotherm. The best linear model is Redlich-Peterson isotherm model, where r2=0,985 and χ2=0,02. In order to predict the error ERRSQ, HYBRD, MPSD, ARE and EABS were used. Moreover, by minimizing these error functions the optimal values of parameters and also the optimum isotherm was found. The Redlich-Peterson isotherm was found to be the best representative for adsorption of Cu(II) on the adsorbent in the cases when ERRSQ, HYBRD, MPSD functions were used. There coefficients of determination are 0.986, 0.985, 0.984, respectively and Chi-square is 0.02 in all cases. Freundlich isotherms which were obtained by minimization of the ERRSQ, HYBRD, MPSD, ARE and EABS function showed very good agreement with experimental data. In all cases the coefficients of determination are greater than 0.91. Besides, it was observed that non-linear isotherm models were better for representation of equilibrium data than linearized models.

Optimization of thiamethoxam adsorption parameters using multi-walled carbon nanotubes by means of fractional factorial design.

The aim of this work was to evaluate significant factors affecting the thiamethoxam adsorption efficiency using oxidized multi-walled carbon nanotubes (MWCNTs) as adsorbents. Five factors (initial solution concentration of thiamethoxam in water, temperature, solution pH, MWCNTs weight and contact time) were investigated using 2V(5-1) fractional factorial design. The obtained linear model was statistically tested using analysis of variance (ANOVA) and the analysis of residuals was used to investigate the model validity. It was observed that the factors and their second-order interactions affecting the thiamethoxam removal can be divided into three groups: very important, moderately important and insignificant ones. The initial solution concentration was found to be the most influencing parameter on thiamethoxam adsorption from water. Optimization of the factors levels was carried out by minimizing those parameters which are usually critical in real life: the temperature (energy), contact time (money) and weight of MWCNTs (potential health hazard), in order to maximize the adsorbed amount of the pollutant. The results of maximal adsorbed thiamethoxam amount in both real and optimized experiments indicate that among minimized parameters the adsorption time is one that makes the largest difference. The results of this study indicate that fractional factorial design is very useful tool for screening the higher number of parameters and reducing the number of adsorption experiments.

New Classes of Weighted Hölder-Zygmund Spaces and the Wavelet Transform

We provide a new and elementary proof of the continuity theorem for the wavelet and left-inverse wavelet transforms on the spaces 𝒮0(ℝn) and 𝒮(ℍn

Varietal phenolic composition of Probus, Rumenika and Frankovka red wines from Fruška Gora (Serbia) and changes in main compounds during maceration

Red wine is a rich source of different phenolic compounds which contribute to sensorial characteristics and can exhibit various biological properties. The amount of phenolics in wine depends on various factors such as grape variety, environmental conditions and production technology. The extraction of individual polyphenolic compounds during maceration was investigated in this paper. Preliminary determination of specific phenolic compositions in wines produced from grape varieties characteristic for Fruška Gora region (Probus, Frankovka and Rumenika) was also performed. A general trend in extraction of some compounds as well as specific characteristics for each variety regarding phenolic composition was observed. Obtained results showed that among wines of different varieties and vintages, statistically significant differences existed in the content of most analysed phenolics. Wines made from Probus variety were characterised by very high anthocyanin content and Frankovka wines by high content of syringic acid while high contents of piceid (resveratrol), catechin and gallic acid were specific for Rumenika variety. Obtained results have shown that Probus variety has especially great winemaking potential considering high content of phenolic compounds (especially anthocyanins), as well as intensive and stable colour.

The wavelet transforms in Gelfand-Shilov spaces

We describe local and global behavior of wavelet transforms of ultra-differentiable functions. The results are given in the form of continuity properties of the wavelet transform on Gelfand–Shilov type spaces and their dual spaces. In particular, we introduce a new family of highly time-scale localized spaces on the upper half-space. We study the wavelet synthesis operator (the left-inverse of the wavelet transform) and obtain the resolution of identity (Calderón reproducing formula) in the context of ultradistributions.

Using the eight-roller mill in the purifier-less mill flow

Double grinding of mill streams without intermediate sieving, i.e. the eight-roller milling system provides opportunities for significant reduction of capital cost compared to conventional wheat flour milling system. In this study the effects of using the eight-roller mill in the purifier-less mill flow were investigated. Middlings from the break system of commercial flour mill, which would be sent to the purification system, were intercepted and employed in the experiments. Milling results obtained with double grinding of middlings were compared with the results obtained by conventional system with intermediate sifting before regrinding of stock. At the same roll gap setting and under the same sieving conditions, the eight-roller system produced less flour compared to the conventional system. Results showed that the most efficient way to increase flour yield in the eight-roller milling system is to increase the upper size limit of flour by increasing the sieve aperture. This is not followed by the deterioration of flour quality as determined by ash content. Increase of the upper size limit of flour particles is followed by the decrease of the flour ash content suggesting that it is possible to implement the eight-roller mills in the purifier-less mill flow.

Application of an original soil tillage resistance sensor in spatial prediction of selected soil properties

Implementation of novel three-point-hitch measuring system.Investigation of potential of new measuring system for better soil observation.Utilization of geostatistics for maps generation of soil physical properties.Study of interactions between soil tillage resistance and standard soil properties. Horizontal and vertical variability of soil properties, temporal dynamics, and the complexity of monitoring and prediction processes are the limiting factors for full implementation of all the postulates of site specific crop management. The aim of this research was to prove the possibilities for utilization of original soil tillage resistance measuring device in spatial assessment of some physical properties of soil.The tillage resistance measurement and soil evaluation were performed in 2012 on a field of 0.78ha, with calcic chernozem type of soil. The year before, the field was divided into three equal plots where three types of tillage were applied (moldboard plowing, disc harrowing and chisel plowing) in order to increase spatial soil differences and to ensure more reliable testing. Soil physical properties were observed at 30 points that were arranged on the nodes of a rectangular grid all over the field along with their geopositioning. Soil tillage resistance was measured in real time and space, during 30 passes that were made on the entire field by a standard tractor and plow.The tillage management applied in 2011 resulted in the differences of some soil parameters. Significant differences between the field plots arose with respect to cone index, moisture content and soil tillage resistance. However, no differences arose regarding the texture (sand, silt+clay content) and bulk density. The correlation analysis showed a high positive correlation between soil resistance and cone index (R=0.82) and a negative correlation between soil resistance and moisture content (R=-0.41). Fitting of variograms in the modeling of spatial correlation gave the highest prediction error for cone index (13.9%), then for tillage resistance (9.32%), sand content (3.95%), moisture content (3.34%), bulk density (2.4%), and finally clay+silt content (2.2%). The generated maps showed that the soil compaction, moisture and tillage resistance had certain orientations with respect to the field plots.

Chemometric optimization of the robustness of the near infrared spectroscopic method in wheat quality control.

A chemometric approach was applied for the optimization of the robustness of the NIRS method for wheat quality control. Due to the high number of experimental (n=6) and response variables to be studied (n=7) the optimization experiment was divided into two stages: screening stage in order to evaluate which of the considered variables were significant, and optimization stage to optimize the identified factors in the previously selected experimental domain. The significant variables were identified by using fractional factorial experimental design, whilst Box-Wilson rotatable central composite design (CCRD) was run to obtain the optimal values for the significant variables. The measured responses included: moisture, protein and wet gluten content, Zeleny sedimentation value and deformation energy. In order to achieve the minimal variation in responses, the optimal factor settings were found by minimizing the propagation of error (POE). The simultaneous optimization of factors was conducted by desirability function. The highest desirability of 87.63% was accomplished by setting up experimental conditions as follows: 19.9°C for sample temperature, 19.3°C for ambient temperature and 240V for instrument voltage.

The function for estimating the separation efficiency of the wheat flour milling process

Considering the significant differencies between the chemical composition of the kernel layers, distribution of chemical compounds in intermediate, final and subproducts of the milling process come as a result of the level of dissociation achieved during the milling process. These differences serve as a basis for the mill process control. Ash determination is probably the most widely used tool while even greater differencies exist in cellulose and especialy starch content. In this work efficiency function has been defined and used to evaluate the relative efficiency of the separation of endosperm from the outer pericarp leyers of the kernel. It is based on quantity rates (flour extraction and subproducts yield) and qulitative analyses (starch and cellulose content in the wheat, flour and subproducts).

Progressive Gelfand-Shilov Spaces and Wavelet Transforms

We discuss progressive Gelfand-Shilov spaces consisting of analytic signals with almost exponential decay in time and frequency variables. It is shown that such signals enjoy an additional localization property. We define wavelet transform and inverse wavelet transform in (progressive) Gelfand-Shilov spaces and study their continuity properties. It is shown that with a slightly faster decay in domain we may control the decay of the wavelet transform independently in each variable.