Taking advantage of the quasiharmonic polynomials for analysis of stationary electromagnetic fields by Trefftz's method

Contents In the paper quasi-harmonic polynomials have been applied for solving the Laplace and Poisson equations by means of Trefftz's method. These polynomials are a generalization of the commonly used harmonic polynomials for field theoretic problems of axial symmetry. The proposed method is illustrated by examples of the analysis of scalar and vector fields having axial symmetry.

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Anwendung der quasiharmonischen Polynome zur Analyse der stationären elektromagnetischen Felder mit Hilfe der Trefftzschen Methode

Übersicht In der Arbeit wird die Anwendung der sogenannten quasiharmonischen Polynome zur Lösung von Aufgaben, die mit Hilfe der Laplaceschen und Poissonschen Gleichungen beschrieben werden, nach der Methode von Trefftz vorgeschlagen. Diese Polynome sind eine Erweiterung der bisher verwendeten harmonischen Polynome auf axialsymmetrische Felder.Die vorgeschlagene Methode wird mit Hilfe von Beispielen über die Analyse von axialsymmetrischen Skalar- und Vektorfeldern veranschaulicht.

     

Analysis of spontaneous electrochemical oscillations by energy distribution technique

Analysis of non-stationary electrochemical oscillations emerges utilization of the techniques allowing an observation of time evolution of their parameters such as instantaneous frequency, amplitude or frequency band. An algorithm of extraction of these parameters can be based on one of linear or quadratic time-frequency representations of oscillations record. In this paper, the authors present representatives of such transformations (Choi-Williams and Cone-shaped) originating from one of the most popular joint time-frequency energy distribution—Wigner-Ville distribution. Short introduction to the mathematics of the topic discussed is provided, then the authors present an example of application in the analysis of current oscillations of copper dissolution process.     

Influence of the Rancimat Apparatus Operating Parameters on Oxidative Stability Determination of Cold-Pressed Camelina and Hemp Seed Oil

The study investigates the impact of operating parameters such as temperature (90, 100, 110, 120 °C), airflow rate (10, 15, 20 L h⁻¹), and sample weight (3, 6, 9 g) on the oxidative stability of cold-pressed camelina and hemp seed oils using the Rancimat apparatus. Conducted analysis indicates a significant influence of temperature on oils' induction time. Moreover, higher airflows should be selected at high analysis temperatures. Based on the calculated parameters of the oxidation kinetics, it was shown that hemp oil has higher activation energy values than camelina oil. Response surface methodology (RSM) indicates that to minimize the determination time of camelina oil oxidation, the following analysis conditions should be selected: sample weight (SW) = 33.5 g, airflow (AF) = 20 L h⁻¹, and temperature (T) = 120 °C. However, for hemp oil, these parameters should be SW = 5.56 g, AF = 15 L h⁻¹, T = 120 °C. Sample mass does not significantly impact oils induction time, which depends mainly on the temperature and airflow. Practical applications: The conducted research shows that the parameters of the cold-pressed camelina and hemp oils oxidative stability have to be determined experimentally. The determined parameters for assessing the oxidative stability will reduce the analysis time and the possibility of interpolating the obtained result at different temperatures and analysis parameters.     

Reduction of fractures in dried clay-like materials due to specific surfactants

The possibility of fracture reduction as a result of application of specific surfactants during intensive drying of clay-like materials was examined in this paper. The dodecyl sulfate sodium salt (SDS) and the fluoric (FC 4430) surfactants were used for the tests. Different amounts of these surfactants were mixed with distilled water and used for wetting a dry clay material before forming clay samples. The clay samples in the form of cylinders 44 mm in diameter and 50 mm high were extruded and after leveling the moisture distribution subjected to convectively drying in hot air at 120 °C. The acoustic emission (AE) method was used to monitor on line the development of crack formation in dried samples. It was stated that application of surfactants in a prescribed amount may significantly reduce the drying induced fractures in clay during its intensive drying and thus to obtain good quality products by high drying rates.     

Sorption Properties of Vacuum-Dried Strawberries

This work demonstrates the influence of changes in parameters of vacuum drying (temperature and pressure) on the sorption properties of dried strawberries. Fruits were dried at 50 and 70°C under pressures of 4 and 16 kPa. Vacuum drying was also conducted during the first 4 h at 70°C and then the temperature was decreased to 50°C at a pressure of 4 kPa. The other combination included increasing the pressure after the first 4 h from 4 to 16 kPa at a drying temperature of 70°C. Sorption isotherms were determined in the dried strawberries. It was shown that with increasing drying temperatures, there was a notable deterioration in the capacity for absorbing water vapor by the vacuum-dried fruit. On the other hand, the pressure at which vacuum drying proceeded did not significantly affect water vapor absorption. Changing the parameters of vacuum drying—that is, temperature in the range of 50–70°C and pressure in the range of 4–16 kPa—affected the shape and structure of the resultant dried strawberries. The combination of vacuum drying with convective drying also influenced the shape and structure of the dried fruit.     

Methylglycinediacetic Acid as a New Complexing Agent for Removal of Heavy Metal Ions from Industrial Wastewater

Sorption is a suitable method for the removal of all contaminants in the ionic form, also including heavy metal ions in the presence of complexing agents from different systems. The aim of this study was a comparison of Cu(II), Ni(II), and Pb(II) sorption in the presence of a complexing agent of a new generation on the strongly basic anion exchangers Amberjet 4200, Amberjet 4600, and Purolite A 520E under different chemical conditions. In the investigation, methylglycinediacetic acid (MGDA), patented by BASF The Chemical Company (Germany) and marketed under the brand name Trilon M, was used. It is a strong complexing agent, readily biodegradable in compliance with Organization for Economic Co-operation and Development (OECD) standards. It was found that the sorption efficiency of strongly basic anion exchangers varied, depending on the metal ions concentration, the pH, the contact time, the temperature, and the properties of anion exchangers, that is, their forms. From the determined breakthrough curves, the distribution coefficients and the ion exchange capacities were calculated. Besides, two different kinetic behaviors were tested for the investigated systems. The experimental data fitted using the Langmuir, Freundlich, and Elovich sorption models, were applied to describe the equilibrium isotherms and determine the isotherm constants. The variations of thermodynamic functions were also calculated.     

SOLID PHASE EXTRACTION FOR PRECONCENTRATION AND SEPARATION OF SELENIUM SPECIES

ABSTRACT

There is sufficient evidence today that selenium is both an essential and toxic element for animal and man. This review article intends to show the involvement of selenium in the environment and in biology. Attention is paid to its occurrence, distribution, sampling and storage and also recent developments for selenium determination reported in analytical literature. Special emphasis is placed on the application of solid sorbents for preconcentration and separation of inorganic and organic selenium species. Published data for these procedures are critically discussed.     

Modeling of Sorption Isotherms of Various Kinds of Wood at Different Temperature Conditions

Adsorption and desorption isotherms of pine, spruce, birch, and willow Salix viminalis v. Orm (2-year stem) under three temperature conditions (20, 50, 75°C) in the range of water activity 0.0–0.9 were studied. In order to describe our experimental data, five models were implemented (GAB, Peleg, Chung-Pfost, Oswin, Halsey) and compared. It was found that GAB and Peleg models provide the best fit to the experimental data. On the basis of GAB modeling, the monolayer moisture content for each kind of wood was calculated. Moreover, the hysteresis phenomenon was investigated. The influence of temperature and wood variety on sorption isotherms was also tested.     

DYNAMIC AND HYBRID NEURAL MODEL OF THERMAL DRYING IN A FLUTDIZED BED

ABSTRACT

A preliminary study aimed at comparing Classical Dynamic Neural Modelling (CDNM) and Hybrid Neural Modelling (HNM) to describe thermal dewatering process in a fluidized bed is presented Two schemes of HN modelling were developed to find the most efficient way of combining a classical mathematical model of the process and Artificial Neural Network (ANN). CDN model was developed using “moving window” technique. In the first scheme of HNM a feed-forward ANN was trained to predict evaporation rate and heat flux in the drying process. In the second scheme of the HN model, ANN was used to determine heat transfer coefficient only. Excellent prediction of drying process by HNM is proved.