Space weathering simulations through controlled growth of iron nanoparticles on olivine

Airless planetary bodies are directly exposed to space weathering. The main spectral effects of space weathering are darkening, reduction in intensity of silicate mineral absorption bands, and an increase in the spectral slope towards longer wavelengths (reddening). Production of nanophase metallic iron (npFe0) during space weathering plays major role in these spectral changes. A laboratory procedure for the controlled production of npFe0 in silicate mineral powders has been developed. The method is based on a two-step thermal treatment of low-iron olivine, first in ambient air and then in hydrogen atmosphere. Through this process, a series of olivine powder samples was prepared with varying amounts of npFe0 in the 7-20 nm size range. A logarithmic trend is observed between amount of npFe0 and darkening, reduction of 1 µm olivine absorption band, reddening, and 1 µm band width. Olivine with a population of physically larger npFe0 particles follows spectral trends similar to other samples, except for the reddening trend. This is interpreted as the larger, ~40-50 nm sized, npFe0 particles do not contribute to the spectral slope change as efficiently as the smaller npFe0 fraction. A linear trend is observed between the amount of npFe0 and 1 µm band center position, most likely caused by Fe2+ disassociation from olivine structure into npFe0 particles.Peer reviewe

Design of experiment for measurement of Langevin function

The presented study focuses on a confrontation of the theory of regression models and theory of experiment with the real situation of determining properties of magnetic (nano)materials. Their magnetic properties can be deduced by measuring their magnetization, being the fundamental magnetic quantity of an arbitrary (nano)material. The results of the magnetization measurements determine the unknown parameters of a known nonlinear function that characterizes the (nano)material under investigation. Knowledge of the values of the unknown parameters enables to decide whether the (nano)material is suitable or not for a particular application. Thus, in this work, we present a possible approach how to estimate the unknown parameters of the nonlinear function by the regression models, taking into account a relevant linearization criterion. Then, we suggest an appropriate design for the measurement to get better estimators of the parameters

Depletion analysis of the HELIOS experiment using the MCB code

The focus of our studies is to present an advanced depletion analysis of the HELIOS experiment by means of the Monte Carlo continuous energy burn-up code (MCB). The MCB was used mainly to calculate nuclide density evolution in nuclear reactor cores. We present the capability of the MCB to investigate the depletion of nuclear fuel samples irradiated in the HELIOS experiment. In our studies we traced the behaviour of the main fissile isotopes, 242mAm and 239Pu, respectively. We also perform a sensitivity analysis to the choice of JEF2.2 and JEFF3.1 cross section libraries in terms of the released fission power and the evolution of actinide inventories. The amount of He produced at the end of irradiation, as well as Am and Pu depletion, were also considered

Determining basic forest stand characteristics using airborne laser scanning in mixed forest stands of Central Europe

This study focused on the derivation of basic stand characteristics from airborne laser scanning (ALS) data, aiming to elucidate which characteristics (mean height and diameter, dominant height and diameter) are best approximated by the variables obtained using ALS data. The height of trees of different species in four permanent plots located in the Slovak Republic was derived from the normalised digital surface model (nDSM) representing the canopy surface, using an automatic approach to identify local maxima (individual treetops). Tree identification was carried out using four different spatial resolutions of the nDSM (0.5 m, 1.0 m, 1.5 m, and 2.0 m) and the number of trees identified was compared with reference data obtained from field measurements. The highest percentage of tree detection (69-75%) was observed at the spatial resolutions of 1.0 and 1.5 m. Absolute differences of tree height between reference and ALS datasets ranged from 0 to 36% at all spatial resolutions. The smallest difference in mean height was obtained using the higher spatial resolution (0.5 m), while the smallest difference in the dominant height of the relative number of thickest trees (h10% and h20%) was observed using the lower spatial resolution (2 m). The same trends also apply to diameters. The average errors at resolution of 1.0 and 1.5 m was 8.7%, 5.9% and 9.7% for mean height, h20% and h10%, respectively. ALS-derived diameters (obtained using regression models from reference data and ALS-derived individual height as predictor) showed absolute errors in the range 0-48% at all spatial resolutions. The deviation in mean diameter at a resolution of 0.5 m ranged from -12.1% to 15.3%

Magnetic Interactions between Nanoparticles Formed during Calcination of Ferrihydrite

Magnetic interactions between nanoparticles of magnetite $Fe_3O_4$ and α-Fe formed during calcination of ferrihydrite in $H_2$ at temperatures 533 ÷ 713 K were studied. The detailed phase analysis describes evolution of contents of magnetite and α-Fe. Explanation of an anomalous course of magnetic moment characterized by a local maximum at an early stage of formation of nanoparticles is discussed