M. Škrátek

Biodegradable polymer nanocomposites based on natural nanotubes: effect of magnetically modified halloysite on the behaviour of polycaprolactone

Abstract The present study explores the effect of a magnetically modified halloysite (mHNT) surface on the structure and properties of biodegradable polymer nanocomposites based on poly ɛ-caprolactone (PCL). Halloysite nanotubes (HNTs) have been modified by a scalable and tunable procedure using magnetic Fe oxide particles prepared by microwave-assisted synthesis from ferrous sulfate at high pH. The HNT content in composites prepared in melt varied from 5 to 30 wt.%. Application of magnetically modified HNT to PCL resulted in the formation of soft magnetic materials. Analyses of the nanocomposite structure revealed that both natural and magnetized HNTs, as well as free magnetite particles are dispersed uniformly in the polymer matrix. Investigation of the mechanical and physical properties confirmed that the reinforcing ability of HNTs was not affected by magnetic modification.

Effects of low-level La doping and ageing on TlPb-1223 high T c superconductors

Bulk samples of the nominal composition of (Tl0.6Pb0.5)(Sr0.8Ba0.2)2Ca2Cu3O8+δ−xLaO1.5 (x = 0–0.1) were prepared by using two-step process and their microstructure, Tc values, and magnetization were studied. The samples consist of the Tl-1223 dominant phase with small Tl-1212 admixture, which increases with a rise of La content. Five years ageing and following oxygen annealing at 450°C and subsequently at 750°C have only a modest effect on Tc values of the studied samples. Low-level La doping (x = 0:04) leads to an increase of Tc values by about 2 K in comparison with undoped samples. Oxygen annealing at 750°C results in an increase in the volume magnetization hysteresis in low applied magnetic fields and rise of critical current density at zero magnetic field and 77 K. This effect is most pronounced for the low La doped sample with x = 0.04. Changes of the induced voltage, U originating in the Meissner effect and of its harmonics in dependence on temperature were measured and used for characterization of the temperature distribution of inter-grain junctions.

Design and Construction of Novel Instrumentation for Low-Field MR Tomography

Abstract Magnetic resonance imaging (MRI) is a very popular tool for diagnostic applications and research studies. Low-field MR scanners, usually with an open design, are suitable for claustrophobic and obese patients, as well as for children, who may be fearful in closed MR scanners. However, these types of scanners provide lower spatial resolution and a lower signal-to-noise ratio (SNR) if compared with the same examination performed at the same time at high field scanners. It is dominantly caused by the low field strength and other factors, such as radiofrequency noise. Therefore, a long measurement time is usually necessary. This research paper is focused on the development of novel probes and preamplifiers for low-field MR scanners to improve SNR, and thus, shorten the measurement time. In this study, we describe the design of a high impedance preamplifier and a high temperature superconductor (HTS) coil. This novel instrumentation was compared with uncooled and cooled copper coils. Improvement in SNR in the case of an HTS coil is reported.

Magnetic halloysite reinforced biodegradable nanofibres: New challenge for medical applications

The work explores preparation of new biocompatible magnetic halloysite nanotubes (MHNTs) reinforced polycaprolactone/gelatine nanofibres. MHNTs were prepared by mixing halloysite nanotubes (HNTs) with microwave-synthesized magnetic iron oxide particles suspension. Electrospun nanofibres comprising 8 wt % poly ɛ-caprolactone (PCL) and 8 wt % gelatine (Gel) have been prepared by using eco-friendly solvent – acetic acid suitable for medical applications. The content of MHNT in PCL/Gel nanofibres was 6.0 and 9.0 wt %. SEM observations revealed that the addition of both, unmodified and magnetic halloysite, significantly affected the polymer mixture spinnability and fibre diameter; however the uniformity and homogeneity of nanofibres were much better in nanofibres with magnetic halloysite. In addition of improved structure, application of MHNTs to PCL/Gel nanofibres resulted in the formation of soft ferromagnetic materials with good response to magnetic field.

Accuracy of the measurement with the second order axial gradiometer

Accuracy of the measurement with the second order axial gradiometer Determining the accuracy of the measurement by using the second order axial gradiometer is presented. Output signals from the SQUID gradiometer system and calculated values of systematic errors depending on the shape and positioning of small cylindrical samples containing magnetized material are introduced. The measurement of the gradiometer detection characteristics and systematic error analysis were accomplished.