Comparative study of radiation-induced damage in magnesium aluminate spinel by means of IL,CL and RBS/C techniques

A comparative study of damage accumulation in magnesium aluminate spinel (MgAl₂O₄) has been conducted using ionoluminescence (IL), cathodoluminescence (CL) and Rutherford Backscattering Spectrometry/channeling (RBS/C) techniques. MgAl₂O₄ single crystal and polycrystalline samples were irradiated with 320 keV Ar⁺ ions at fluencies ranging from 1 × 10¹² to 2 × 10¹⁶ cm^?2 in order to create various levels of radiation damage. RBS/C measurements provided quantitative data about damage concentration in the samples. These values were then compared to the luminescence measurements. The results obtained by IL and RBS/C methods demonstrate a two-step character of damage buildup process. The CL data analysis points to the three-step damage accumulation mechanism involving the first defect transformation at fluencies of about 10¹³ cm^?2 and second at about 10¹⁵ cm^?2. The rate of changes resulting from the formation of nonluminescent recombination centers is clearly nonlinear and cannot be described in terms of continuous accumulation of point defects. Both, IL and CL techniques, appear as new, complementary tools bringing new possibilities in the damage accumulation studies in single- and polycrystalline materials.     

Pleurozium schreberi as bioindicator of mercury pollution in heavily industrialized region

This research is continuation of the investigation of metal accumulation in native and transplanted moss Pleurozium schreberi in the most industrialized and affected region in Poland (Upper Silesia). We tested the hypotheses that in Upper Silesia transplants of P. schreberi may be used in a 90 days bioindication experiment in case native specimens are absent; a 90 days exposure of transplanted P. schreberi was long enough for evaluation of Hg pollution of the environment. An assay was carried out with native mosses at 27 polluted sites and mosses from an uncontaminated control site transplanted to the same 27 polluted sites. P. schreberi collected from the same sites as classified for more and less polluted basing on Pb and Zn concentrations show quite different pattern of pollution with mercury; The accumulation of Hg by the transplants increased much faster in the first 45 days of the experiment (accumulation factor 1.5–6.7; mean 3.4?±?0.5) in comparison with the second period from day 45 to 90 (accumulation factor 1.0–1.6; mean 1.2?±?0.1). The 90 days exposure of transplanted P. schreberi was long enough for evaluation of Hg pollution of the environment. Transplants of P. schreberi may be used in a 90 days bioindication experiment in case native specimens are absent.     

The first record of Cuon alpinus (Pallas, 1811) from Poland and the possible impact of other large canids on the evolution of the species

The presence of Cuon alpinus in Poland is documented here for the first time. Between 650 and 450 ka, Lycaon lycaonoides dominated the open lands, while Cuon alpinus priscus tended to prefer forests, mountains and highlands. Canis mosbachensis coexisted in all these environments. Between 480 and 430 ka, there was a drastic reduction in the number and range of L. lycaonoides. The balance between canids was disturbed and a critical point in the lycaon–wolf relationship was passed. Probably between 450 and 400 ka, the lycaon was too rare to be a real competitor and a limiting factor for the wolf. It was also at this time that the lycaon disappeared completely. With disappearance of the lycaon from Eurasia, there was a slow increase in the body size of the wolf. Between 400 and 300 ka, the dhole and the wolf were still close in body size, but the wolf was slowly increasing in size. Between 300 and 250 ka, the wolf became the dominant dog species and took a niche occupied until then by the lycaon. Because of competition, C. alpinus decreased in body size and adapted to hunting and living in forest, mountain and highland environments.     

Seismic event near Jarocin (Poland)

The earthquake of magnitude M _L = 3:8 (EMSC) took place on Friday, 6 January 2012, north-east of the town of Jarocin in Wielkopolska Region, Poland. The only historical information about past earthquakes in the region was found in the diary from 1824; apart of it, there was a seismic event noticed in the vicinity of Wielkopolska in 1606 (Pagaczewski 1982). The scope of this paper is to describe the 6 January 2012 event in view of instrumental seismology, macroseismic data analysis and known tectonics of the region, which should be useful in future seismic hazard analysis of Poland.     

Geodetic VLBI with an artificial radio source on the Moon: a simulation study

We perform extensive simulations in order to assess the accuracy with which the position of a radio transmitter on the surface of the Moon can be determined by geodetic VLBI. We study how the quality and quantity of geodetic VLBI observations influence these position estimates and investigate how observations of such near-field objects affect classical geodetic parameters like VLBI station coordinates and Earth rotation parameters. Our studies are based on today’s global geodetic VLBI schedules as well as on those designed for the next-generation geodetic VLBI system. We use Monte Carlo simulations including realistic stochastic models of troposphere, station clocks, and observational noise. Our results indicate that it is possible to position a radio transmitter on the Moon using today’s geodetic VLBI with a two-dimensional horizontal accuracy of better than one meter. Moreover, we show that the next-generation geodetic VLBI has the potential to improve the two-dimensional accuracy to better than 5 cm. Thus, our results lay the base for novel observing concepts to improve both lunar research and geodetic VLBI.     

Investigation of the 16-year and 18-year ZTD Time Series Derived from GPS Data Processing

The GPS system can play an important role in activities related to the monitoring of climate. Long time series, coherent strategy, and very high quality of tropospheric parameter Zenith Tropospheric Delay (ZTD) estimated on the basis of GPS data analysis allows to investigate its usefulness for climate research as a direct GPS product. This paper presents results of analysis of 16-year time series derived from EUREF Permanent Network (EPN) reprocessing performed by the Military University of Technology. For 58 stations Lomb-Scargle periodograms were performed in order to obtain information about the oscillations in ZTD time series. Seasonal components and linear trend were estimated using Least Square Estimation (LSE) and Mann—Kendall trend test was used to confirm the presence of a linear trend designated by LSE method. In order to verify the impact of the length of time series on trend value, comparison between 16 and 18 years were performed.     

Geomorphic and hydrological controls on groundwater dolocrete formation in the semi-arid Hamersley Basin,northwest Australia

Groundwater dolocretes may exert an important geomorphic control on landscape evolution within sub-humid to arid regions. However, the geomorphic and hydrogeological settings of dolocrete remain poorly described. The hydrochemical conditions of dolomite precipitation in groundwater environments are also not well known. Classic models of dolocrete formation explain dolomite precipitation from highly evolved groundwaters at the terminus of major drainage but do not explain dolocrete distributed in regionally elevated landscapes, upgradient of major drainage. This study investigated the mineralogy, micromorphology and stable carbon and oxygen isotope compositions of three dolocrete profiles within a regionally elevated sub-basin of the Hamersley Ranges in the Pilbara region of northwest Australia. We sought to establish the environmental and hydrochemical conditions and present a model for dolocrete formation. We found that dolocrete formed within zones of emerging groundwater under saline-evaporitic conditions within internally draining sub-basins, most likely during the Late Miocene and Pliocene. Saline-evaporitic conditions were indicated by: (i) the mineralogy, dominated by dolomite, palygorskite and smectite; (ii) desiccation features and the presence of phreatic and vadose cements, indicative of a shallow fluctuating water table, and; (iii) dolomite δ¹⁸O values (median = –5.88 ‰). Dolomite precipitation was promoted by evaporation and carbon dioxide degassing from shallow magnesium (Mg)-rich groundwater. These factors appear to have been the major drivers of dolocrete development without a requirement for significant down-dip hydrochemical modification. Primary dolomite precipitation was possible due to the presence of microbial extracellular polymeric substances (EPS). EPS provided negatively charged nucleation sites, which bound Mg²⁺, overcoming kinetic effects. High microbial activity within groundwater systems suggest these processes may be important for dolocrete formation worldwide and that groundwater dolocretes may be more pervasive in landscapes than currently recognized. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.     

How selection and weighting of astrometric observations influence the impact probability. The case of asteroid (99942) Apophis

The aim of this paper is to show that in the case of a low probability of asteroid collision with the Earth, the appropriate selection and weighting of the data are crucial for the impact investigation and for analysing the impact possibilities using extensive numerical simulations. By means of the Monte Carlo special method, a large number of 'clone' orbits have been generated. A full range of orbital elements in the six-dimensional parameter space, that is, in the entire confidence region allowed by the observational material, has been examined. On the basis of 1000 astrometric observations of (99942) Apophis, the best solutions for the geocentric encounter distance of  6.065 ± 0.081 R_⊕  (without perturbations by asteroids) or  6.064 ± 0.095 R_⊕  (including perturbations by the four largest asteroids) were derived for the close encounter with the Earth on 2029 April 13. The present uncertainties allow for special configurations ('keyholes') during this encounter that may lead to very close encounters in future approaches of Apophis. Two groups of keyholes are connected with the close encounter with the Earth in 2036 (within the minimal distance of  5.7736−5.7763 R_⊕  on 2029 April 13) and 2037 (within the minimal distance of  6.3359–6.3488 R_⊕  ). The nominal orbits for our most accurate models run almost exactly in the middle of these two impact keyhole groups. A very small keyhole for the impact in 2076 has been found between these groups at the minimal distance of 5.97347   R_⊕  . This keyhole is close to the nominal orbit. The present observations are not sufficiently accurate to eliminate definitely the possibility of impact with the Earth in 2036 and for many years after.