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1
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Influence of Magnetic Field on Dielectric Breakdown in Transformer Oil Based Ferrofluids

100%
Rajňák M., Dolník B., Marton K., Tomčo L., Molčan M., Kopčanský P., Timko M.
Acta Physica Polonica A
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2014
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vol. 126
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issue 1
248-249
EN
In this paper the experimental study of the breakdown field strength in a transformer oil based ferrofluid is reported. The experiments are conducted on five ferrofluid samples with different magnetic volume fraction. The influence of external magnetic field on the breakdown field strength is investigated, when a quasi-homogenous magnetic field was applied in parallel and perpendicular configuration in regard to the electric field. The obtained results are analysed in accordance to the electron charging of ferrofluid nanoparticles theory.
2
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Properties of Magnetosome Suspension under the Influence of Magnetic Field

84%
Józefczak A., Molčan M., Rozynek Z., Hornowski T., Skumiel A., Timko M., Tóthová J., Kopčanský P., Leszczyński B.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
629-631
EN
The magnetotactic bacteria synthesize chains of nanosized magnetic particles that function as a compass needle to navigate in the direction of the earth's magnetic field. Magnetosomes are bacterial magnetic nanoparticles containing iron mineral crystals of magnetite or greigite, enveloped by a natural biological membrane. The objective of the work is to study the influence of magnetic field on rheology and acoustic properties of magnetosome suspension. Experimental results show a clear effect of the external magnetic field on the acoustic parameters such as velocity and attenuation of ultrasonic wave, and the viscosity of the suspension, arising from the biogenic magnetic particles aggregation.
3
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Characterization of Magnetosomes After Exposure to the Effect of the Sonication and Ultracentrifugation

84%
Molčan M., Hashim A., Kováč J., Rajňák M., Kopčanský P., Makowski M., Gojzewski H., Molokáč M., Hvizdák L., Timko M.
Acta Physica Polonica A
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2014
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vol. 126
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issue 1
198-199
EN
Magnetosomes are intracellular organelles of widespread aquatic microorganisms called Magnetotactic bacteria. At present they are under investigation especially in biomedical applications. This ability depends on the presence of intracellular magnetosomes which are composed of two parts: first, nanometer-sized magnetite (Fe_{3}O_{4}) or greigite (Fe_{3}S_{4}) crystals (magnetosome crystal), depending on the bacterial species; and second, the bilayer membrane surrounding the crystal (magnetosome membrane). The magnetosomes were prepared by biomineralization process of magnetotactic bacteria Magnetospirillum Magnetotacticum sp. AMB-1. The isolated magnetosome chains (sample M) were centrifugated at speed of 100000 rpm for 4 hours (sample UM) and sonicated at power of 120 W for 3 hours (sample SM), respectively. The prepared suspensions were investigated with respect to morphological, structural and magnetic properties. The results from scanning electron microscopy showed that isolated chains of magnetosomes were partially broken to smaller ones after ultracentrifugation. On the other hand the application of the sonication process caused the formation of individual magnetosomes (unordered in chain). These results were confirmed by coercivity and magnetization saturation measurements.
4
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The Influence of Morphology on Magnetic Properties of Magnetosomes

84%
Hashim A., Molčan M., Kovač J., Varchulová Z., Gojzewski H., Makowski M., Kopčansky P., Tomori Z., Timko M.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1250-1252
EN
Cultivation process was changed three times. The culture medium was enriched by more amount ferric quinate (FQ magnetosomes sample) and more amounts Wolfe's vitamin solution (WVS magnetosomes sample) comparing to normal culture medium (NP magnetosomes sample). NP sample of magnetosomes shows zero coercivity and behaves superparamagnetically. The increase of coercivity (6.5 Oe for WVS and 20 Oe for FQ) may be caused by higher value of shape anisotropy and reveals stronger magnetic correlations between particles of magnetite chains.
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