Peculiarities of Monitoring the State of a Flowing Medium by the Method of Nuclear Magnetic Resonance

Technical Physics Letters - Specific features of monitoring the state of a flowing medium by method of nuclear magnetic resonance (NMR) are considered. An approach to studying the state of a...     

Rheological and dielectrical characterization of melt mixed polycarbonate-multiwalled carbon nanotube composites

A series of composites of polycarbonate (PC) with 23 different contents of multiwalled carbon nanotubes (MWNT) was produced by melt mixing using the masterbatch dilution method. In dielectric measurements, AC conductivity and complex permittivity data obtained in the frequency range between 10⁻³ and 10⁷ Hz at room temperature indicated the electrical percolation threshold at about 1.0 wt%.

The dynamic mode melt rheological measurements for the same samples at eight temperatures between 170 and 280 °C showed a visible change in the frequency dependence of dynamic moduli and the absolute value of the complex viscosity |η*| particularly at low frequencies. In literature these changes are sometimes related to so called ‘percolation threshold concentration’. Applying this picture to our experimental data we have to assume that the percolation threshold is strongly dependent on the measurement temperature. It changes from about 5 to 0.5 wt% MWNT by increasing the measurement temperature from 170 to 280 °C, respectively. This temperature dependence cannot be explained by a classical liquid-solid transition but may be related to the existence of a combined nanotube-polymer network.     

Spin echo processor in functional electronic devices: Control of responses in processing of multipulse trains

A specific analog device (spin echo processor) is proposed for processing of pulsed data in functional electronic devices under certain conditions. It is shown that a disadvantage of such devices related to generation of multiple noise signals upon processing of multipulse trains can be eliminated with the aid of magnetically ordered working substance using an additional channel that forms magnetic field in the working substance.     

Microdosimetric spectra and LET distributions on board the Mir space station obtained with a particle track detector

A spectrometer measuring energy lost (deltaE) was used to determine linear energy transfer (LET) spectra on board the Mir orbital station during the period from 8 October 1997 to 16 June 2000, i.e. during the 24th, 26th, 27th and 28th basic expeditions. It was found that the LET spectra of secondary particles between 10 and 700 keV.microm(-1) in tissue do not depend on the external radiator, with the average quality factors for the region mentioned being about 6.4 with ICRP 26 quality factors or about 7.4 with ICRP 60 quality factors. Both differential and integral LET spectra are presented for some typical cases. The spectra permitted us to calculate the total doses and dose equivalents due to particles with the LET values in the mentioned region. It was found that these doses are higher when the detector was placed in a less shielded area. It was also found that these doses vary from one expedition to another. The correlation of these variations with the solar activity level was studied.     

Corundum/lanthanum hexaaluminate/alumina nanofiber ceramic composite

We describe a corundum-matrix ceramic composite loaded with layered lanthanum hexaaluminate microparticles and reinforced with alumina nanofibers. The components of the composite are prepared by sol-gel processing. Scanning electron microscopy results indicate that the microparticles and nanofibers are uniformly distributed over the matrix. Surface-modified alumina nanofibers are shown to have the best effect on the strength of the matrix.     

Estimated radiation shielding for a manned flight to mars

Journal Variant of Report IAF/IAA-90-544 at the 41st Congress of the International Astronautical, Federation, Dresden, East Germany, 6-1 October 1990.     

Anisotropy of the Thermal Conductivity of Parahydrogen Crystals

The anisotropy of thermal conductivity of parahydrogen crystals has been observed for the first time. The thermal conductivity measurements have been made on samples of different diameters at the temperature range from 2 to 8 K.