Krešimir Malarić

Effects of radiofrequency electromagnetic fields on seed germination and root meristematic cells of Allium cepa L.

The effects of exposure to radiofrequency electromagnetic fields (RF-EMFs) on seed germination, primary root growth as well as mitotic activity and mitotic aberrations in root meristematic cells were examined in Allium cepa L. cv. Srebrnjak Majski. Seeds were exposed for 2h to EMFs of 400 and 900MHz at field strengths of 10, 23, 41 and 120Vm(-1). The effect of longer exposure time (4h) and field modulation was investigated at 23Vm(-1) as well. Germination rate and root length did not change significantly after exposure to radiofrequency fields under any of the treatment conditions. At 900MHz, exposures to EMFs of higher field strengths (41 and 120Vm(-1)) or to modulated fields showed a significant increase of the mitotic index compared with corresponding controls, while the percentage of mitotic abnormalities increased after all exposure treatments. On the other hand, at 400MHz the mitotic index increased only after exposure to modulated EMF. At this frequency, compared with the control higher numbers of mitotic abnormalities were found after exposure to modulated EMF as well as after exposure to EMFs of higher strengths (41 and 120Vm(-1)). The types of aberration induced by the EMFs of both frequencies were quite similar, mainly consisting of lagging chromosomes, vagrants, disturbed anaphases and chromosome stickiness. Our results show that non-thermal exposure to the radiofrequency fields investigated here can induce mitotic aberrations in root meristematic cells of A. cepa. The observed effects were markedly dependent on the field frequencies applied as well as on field strength and modulation. Our findings also indicate that mitotic effects of RF-EMF could be due to impairment of the mitotic spindle.

Oxidative and genotoxic effects of 900 MHz electromagnetic fields in the earthworm Eisenia fetida

Accumulating evidence suggests that exposure to radiofrequency electromagnetic field (RF-EMF) can have various biological effects. In this study the oxidative and genotoxic effects were investigated in earthworms Eisenia fetida exposed in vivo to RF-EMF at the mobile phone frequency (900 MHz). Earthworms were exposed to the homogeneous RF-EMF at field levels of 10, 23, 41 and 120 V m(-1) for a period of 2h using a Gigahertz Transversal Electromagnetic (GTEM) cell. At the field level of 23 V m(-1) the effect of longer exposure (4h) and field modulation (80% AM 1 kHz sinusoidal) was investigated as well. All exposure treatments induced significant genotoxic effect in earthworms coelomocytes detected by the Comet assay, demonstrating DNA damaging capacity of 900 MHz electromagnetic radiation. Field modulation additionally increased the genotoxic effect. Moreover, our results indicated the induction of antioxidant stress response in terms of enhanced catalase and glutathione reductase activity as a result of the RF-EMF exposure, and demonstrated the generation of lipid and protein oxidative damage. Antioxidant responses and the potential of RF-EMF to induce damage to lipids, proteins and DNA differed depending on the field level applied, modulation of the field and duration of E. fetida exposure to 900 MHz electromagnetic radiation. Nature of detected DNA lesions and oxidative stress as the mechanism of action for the induction of DNA damage are discussed.

Rigorous analysis on performance of LEO satellite ground station in urban environment

Since two decades the microsatellites in Low Earth Orbits (LEO) are in use. Low Earth Orbit satellites are used for public and massive communication and for scientific purposes, also. Low Earth Orbits vary with the type of satellites and their primarily purposes. Low Earth Orbit scientific satellites have very wide application, including Earth’ s surveillance and astronomy applications. These satellites provide opportunity for investigations for which existing techniques are either difficult or impossible to be applied. Thus, it is to be expected that such missions in the near future will be more developed especially in the fields where similar experiments can not be done by means on the Earth. So, also the ground stations have to be established in order to communicate with such satellites. The quality of communication depends on the performance of the satellite ground station, also. Before the implementation of the ground station the analyses related to environmental factors have to be considered, especially in urban areas. Rain effects, intermodulation products disturbance, contact time duration at low elevation, are few aspects which are considered in this work related to final decision on design of the ground station. The performance measurement of the ground station based on Sun flux density is described as an experimental method which provides opportunity to check the performance of the ground station.

Absorber and resistor contribution in the GTEM-cell

The GTEM-cell is described. The influence of absorbers and resistors is shown. The SWR and return loss as well as time domain measurements were performed on the GTEM-cell as well as on GTEM-cell without resistors, absorbers, and with open and metal end. The obtained data was, compared and the conclusion drawn. The GTEM-cell was modeled with the FEM method as well.

Measured distribution of electric field in GTEM-cell

The electric field inside the GTEM-cell was measured with the field probe. The variation of the electric field was within 3 dB. The measured results were compared with the numerical model performed with finite element method (FEM). There is a very good agreement between measured results and the computer model. Both results prove that almost 80% of the area below septum could be used for testing purposes.

Composite Noise Temperature at Low Earth Orbiting Satellite Ground Station

Noise introduces a fundamental limit on the performance of any communication system. Satellite communication systems are particularly susceptible to noise because of their inherent low received power. During the link budget calculations, noises of the equipment and line loss have to be considered. An alternative, but equivalent way of expressing the noisiness of the equipment and line loss is through noise temperature. The noise temperature which represents noise of all components in satellite receiving system chain is called composite noise temperature. Thus, on this paper the methodology applied for composite noise temperature calculations for satellite links is presented. In order to illustrate these calculations, data of Vienna ground station within MOST project are applied. The project MOST (microvariability and oscillations of stars) is a Canadian micro satellite space telescope mission. The project MOST consists of a low earth orbiting (LEO) satellite and three ground stations, one of them in Vienna. The Vienna ground station system was set up at the Institute for Astronomy of the University of Vienna in cooperation with the Institute of Communications and Radio-Frequency Engineering of the Vienna University of Technology. The satellite link operates on 2 GHz band

Measurement of GSM phone emission

GSM (Global System for Mobile Communications) phones are part of everyday life. Their emission level is an EMC (Electro-Magnetic Compatibility) issue. It is important to know the peak of signal levels of the mobile phones. They can cause interference with other electronic devices. The emission testing was performed in GTEM-cell (Giga-Hertz Transversal Electromagnetic mode). The measured peak powers in various regimes of the operation were 15.1 mW for conversation and 2 W for ringing and SMS (short message service) message. Use of GSM mobile phones should be used carefully in the vicinity of electronic devices and systems.

A nonlinear least-squares graphical tool ('Gaussfit') for educational purposes

This paper describes a computer program that finds a function which closely approximates experimental data using the least-squares method. The program finds parameters of the function as well as their corresponding uncertainties. It also has a subroutine for graphical presentation of the input data and the function. The program is used for educational purposes at undergraduate level for students who are learning least-squares fitting, how to solve systems of linear equations and about computer calculation errors.

Voltage ratio measurements using two digital voltmeters and resistive voltage divider

This paper presents a method to accurately measure voltage ratios from 1:2 to 1:10 with a calibrated digital voltmeter (DVM) at voltage ranges of 1-10 V using a simple resistive-voltage divider. The divider can be used as an absolute divider or as a Hamon divider. The achieved accuracy is better than 10/sup -7/, comparable to those reported with measurements with Josephson array voltage source (JAVS).

Set-up for testing telecom power unit immunity to electromagnetic fields

Modern telecommunications facilities depend on power units, which can be shut down suddenly by severe disturbances. A large number of disturbances can be attributed to radiated electromagnetic emissions. Emission testing has been relatively easy. The immunity of electronic equipment to RFI is expressed as maximum electric field strength that it can withstand. The paper describes the respective test set-up. Besides standard measuring equipment like RF generators and power amplifiers, a cell is needed in which well defined electromagnetic field is established. The cell was used to test a DC/DC converter. The paper exhibits the test procedure.