A man is exposed to electromagnetic fields in his environment. Electromagnetic fields always exist in nature – atmospheric static electric field, the Earth's magnetic static field, the fields of a wide range of frequencies due to the outbreaks in the atmosphere, etc. However, a man is today the most exposed to the artificial field, due to progress in technology and widespread use of electrical devices. Currents, induced by electric field of surface charges are the greatest if external electric field is parallel to the length of the body. Magnetic field induces a currents inside the body as well. Variable magnetic field acting by force on charged particles in the body and creates eddy currents according to Faraday's law. Such induced currents in the low frequency area can stimulate electrically excitable tissues, such as nerve and muscle fibers, through the mechanism of action potential triggering. The area of occupational exposure includes people who are exposed to electromagnetic fields in known circumstances during usual performing of work tasks in and around power facilities, but they are educated to take protective measures and they have all the tools and instructions provided. These people are aware of potential risks and take appropriate protective measures. The environment around the power facility falls within the area of increased sensitivity, which includes people of different ages and health conditions, including those particularly sensitive. In many cases people are not aware of exposure to electromagnetic fields and can not be expected to take protective measures to reduce exposure. Therefore, the restrictions for that area are stricter than those for area of occupational exposure. The most efficient way for reliable operation of the devices in high voltage substation is the calculation and measurement of low frequency electromagnetic fields in the substation, together with appropriate measurement procedure. Contemporary research of electromagnetic fields is based on the concept that complex theoretical research results in appropriate design solution, and developes almost exclusively as applied research. Generally, there are two directions; the first one based on calculation model development, and the second one based on models of objectivized physical measurements in hard conditions. In both cases, the goal is the same and can be summarized as follows: create the

Most of medical journals now has it’s electronic version, available over public networks. Although there are parallel printed and electronic versions, and one other form need not to be simultaneously published. Electronic version of a journal can be published a few weeks before the printed form and must not has identical content. Electronic form of a journals may have an extension that does not contain a printed form, such as animation, 3D display, etc., or may have available fulltext, mostly in PDF or XML format, or just the contents or a summary. Access to a full text is usually not free and can be achieved only if the institution (library or host) enters into an agreement on access. Many medical journals, however, provide free access for some articles, or after a certain time (after 6 months or a year) to complete content. The search for such journals provide the network archive as High Wire Press, Free Medical Journals.com. It is necessary to allocate PubMed and PubMed Central, the first public digital archives unlimited collect journals of available medical literature, which operates in the system of the National Library of Medicine in Bethesda (USA). There are so called on- line medical journals published only in electronic form. It could be searched over on-line databases. In this paper authors shortly described about 30 data bases and short instructions how to make access and search the published papers in indexed medical journals.

UDK 577.164.2:582.711.714           535.234:577.164.2 Vitamin C or ascorbic acid content has been determined by spectrophotometric method in fruits of some Bosnian hawthorns (Crataegus L). species. Spectrophotometric method used in this study is based on the kinetic reaction between Vitamin C and methylene blue. Measurements were carried out at absorption maximum, λmax= 665 nm. Titrimetric method was used as the reference method for comparison of the obtained results. We found that the lowest content of vitamin C was 106.12 mg/100 g of a dry sample in fruits of the C. monogyna, and the highest level of Vitamin C was found in the C. microphylla (231.96 mg/100 g of a dry sample) fruits. Recoveries of the results obtained by the spectrophotometric method were 101.4% - 108.0% with relative standard deviation (RSD) values ranging between 0.40% - 3.37%. Obtained results showed that fruits of studied Crataegus L. species are a good source of vitamin C with its potential to be used in food industry as the natural antioxidant.

Abstract The theoretical titration curve of a weak acid with a strong base was considered. The limitation of the Henderson-Hasselbalch equation for the calculation of pH in the buffer region was discussed. One novel simple equation for the exact calculation of pH from the beginning of titration up to the equivalence point was derived. By using this equation with one implicit approximation (the dissociation of water), the calculation of pH values after each addition of titrant is possible. A novel equation provides the simple and exact calculation of pH in the range of buffer, and that can be done in a simple and logical way without complex handling of acid-base equilibrium with computer and spreadsheet software. The calculated titration curves for different concentrations of acetic acid and sodium hydroxide were shown.