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1

Structure of ovaries and formation of egg envelopes in the stonefly, Leuctra autumnalis Aubert, 1948 (Plecoptera: Leuctridae). Ultrastructural studies

100%
Poprawa I., Baran A., Rosciszewska E.
Folia Biologica
|
2002
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vol. 50
|
issue 1-2
29-38
EN
The investigation of ovaries and the formation of egg envelopes of the stonefly Leuctra autumnalis was carried out with light and transmission electron microscopes. The ovary of the studied species is paired and consists of several dozen panoistic ovarioles opening individually to the oviduct. The process of egg capsule formation already begins in previtellogenesis. At this time the follicular cells secrete precursors of the vitelline envelope. Analysis of the presented data suggests that the oocyte itself also takes part in the formation of the vitelline envelope during late vitellogenesis. Simultaneously, the follicular cells produce precursors of further layers of the egg capsule, i.e. two-layered chorion and extrachorion, consisting of two gelatinous layers and a flocculent one. The completely developed capsule contains channels, probably micropylar ones.
2
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Solid State ¹³C Nuclear Magnetic Resonance Study of Morphology and Molecular Mobility in Quenched Poly(3-hydroxybutyrate)

100%
Baran A., Vrábel P., Olčák D.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1144-1146
EN
Single pulse magic angle spinning ¹³C NMR spectra and the carbon spin-lattice relaxation times T₁(¹³C) were used for the study of morphology and molecular mobility in poly(3-hydroxybutyrate) quenched in cold water after melting in a twin-screw extruder. The crystallinity of the quenched sample was found to be comparable with that of virgin material, and the decrease in dimensions of the crystallites grown after quenching was deduced from the single pulse magic angle spinning ¹³C NMR spectra. The spin-lattice relaxation curves for the carbons of the CO, CH, CH₂ and CH₃ groups were found to be bi-exponential, which enables the molecular mobility within crystalline and amorphous domains to be studied. The spin-lattice relaxation times T₁(¹³C) estimated for the carbons of the CO, CH, CH₂ groups show the chain mobility enhancement within crystalline domains of the quenched sample, but the influence of the quenching on the CH₃ group rotation and on the main chain motion within amorphous regions was not observed.
3
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Thermodynamic and Magnetotransport Properties of High Quality Na_{0.77}CoO_{2} Single Crystals

88%
Baran A., Zorkovská A., Kajňaková M., Lin C., Feher A.
Acta Physica Polonica A
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2014
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vol. 126
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issue 1
360-361
EN
Heat capacity and electrical resistivity of high-quality Na_{0.77}CoO_{2} single crystals was systematically studied as a function of temperature and magnetic field. Anomalies at 20 K have been observed both in the heat capacity and the electrical resistivity. The broad bump in the heat capacity indicates a smeared magnetic phase transition. Magnetic fields up to 9 T, oriented perpendicularly to the ab plane, reduce the temperature of this anomaly in accordance with the assumption of A-type antiferromagnetic ordering. The low temperature upturn observed in resistivity below 20 K for slow cooling is also suppressed by the magnetic field. This anomaly is probably the consequence of the interplay of several different mechanisms, including the Kondo effect, electron-electron interactions, and electron-phonon scattering.
4
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Magnetotransport Properties of CaTi_xRu_{1-x}O_3 (x=0, 0.07)

76%
Zorkovská A., Baran A., Feher A., Šebek J., Šantavá E., Bradarić I.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
351-354
EN
Electrical resistance, transversal magnetoresistance and the Hall effect were studied on polycrystalline CaTi_xRu_{1-x}O_3 (x=0, 0.07) samples using a conventional Quantum Design PPMS-9 equipment in the temperature range 2-300 K and magnetic field up to 9 T. Substantial differences were found between the two samples: (i) opposite to the metallic character of CaRuO_3, the substituted sample has insulating-like electrical resistance;(ii) the magnetoresistance of the substituted sample changes the sign from negative to positive values with increasing temperature. The magnetoresistance of CaRuO_3 is negative, the sign reversal is induced by magnetic field and only at temperatures below 15 K, such a behaviour is predicted for clustered systems;(iii) the Hall voltage in pure CaRuO_3 also changes sign from negative to positive values above 35 K. This temperature coincides with the observed magnetic transition temperature, indicating that the magnetic state and the carrier character interrelate.
5
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Ti-Induced Ferromagnetism and the Specific Heat of CaTi_xRu_{1-x}O_3 (x=0, 0.005, 0.03)

76%
Zorkovská A., Baran A., Kajňaková M., Feher A., Šebek J., Šantavá E., Bradarić I.
Acta Physica Polonica A
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2008
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vol. 113
|
issue 1
355-358
EN
The influence of Ti substitution on the specific heat of the CaTi_xRu_{1-x}O_3 system at low concentrations x=0, 0.005, and 0.03 was studied in the temperature range of 2-300 K at magnetic fields up to 9 T. Small peak was revealed in the C/T vs. T^2 dependence at around 3 K, which are field sensitive (the electronic specific heat coefficient γlinearly decreases with the increase in magnetic field), and might be connected to some kind of magnetic ordering. The coefficient γis suppressed also by Ti substitution.
6
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Low Temperature Anomalies in the Specific Heat and Magnetic Susceptibility of Na_{0.7}CoO_2 Samples

64%
Baran A., Zorkovská A., Feher A., Šebek J., Šantavá E., Hejtmánek J., Veverka M., Bradarić I., Ružička M.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
495-498
EN
We present a comparative study of Na_{0.7}CoO_2 samples obtained from three different sources and prepared by different methods. The specific heat and magnetic susceptibility measurements in the temperature range 2-300 K show substantial influence on the observed anomalies, which underlines that the system is extremely sensitive to preparation protocols.
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