Hydrogen bonding in coquimbite, nominally Fe2(SO4)3·9H2O, and the relationship between coquimbite and paracoquimbite     

Juraj Majzlan  Tamara Ðorđević  Uwe Kolitsch  Jürg Schefer 《Mineralogy and Petrology》2010,100(3-4):241-248

Using single-crystal X-ray diffraction at 293, 200 and 100 K, and neutron diffraction at 50 K, we have refined the positions of all atoms, including hydrogen atoms (previously undetermined), in the structure of coquimbite ( $ P {\bar 3}1c $ , a?=?10.924(2)/10.882(2) Å, c?=?17.086(3) / 17.154(3) Å, V?=?1765.8(3)/1759.2(5) ų, at 293 / 50 K, respectively). The use of neutron diffraction allowed us to determine precise and accurate hydrogen positions. The O–H distances in coquimbite at 50 K vary between 0.98 and 1.01 Å. In addition to H₂O molecules coordinated to the Al³⁺ and Fe³⁺ ions, there are rings of six “free” H₂O molecules in the coquimbite structure. These rings can be visualized as flattened octahedra with the distance between oxygen and the geometric center of the polyhedron of 2.46 Å. The hydrogen-bonding scheme undergoes no changes with decreasing temperature and the unit cell shrinks linearly from 293 to 100 K. A review of the available data on coquimbite and its “dimorph” paracoquimbite indicates that paracoquimbite may form in phases closer to the nominal composition of Fe₂(SO₄)₃·9H₂O. Coquimbite, on the other hand, has a composition approximating Fe_1.5Al_0.5(SO₄)₃·9H₂O. Hence, even a “simple” sulfate Fe_2-x Al _x (SO₄)₃·9H₂O may be structurally rather complex.  相似文献   

Motion of a Meteoroid Released from an Asteroid     

Peter Vereš  Jozef Klačka  Ladislav Kómar  Juraj Tóth 《Earth, Moon, and Planets》2008,102(1-4):47-51

Evidence of asteroid surface features as regolith grains and larger boulders implies resurfacing possibility due to external forces such as gravitational tidal force during close planet encounters. Motion of a meteoroid released from an asteroid in the gravitational fields of the asteroid and the Earth is modeled. We are interested mainly in a distance between the meteoroid and the asteroid as a function of the time. Applications to Itokawa and some close approaching NEAs are presented.  相似文献   

RTM-based omission error corrections for global geopotential models: Case study in Central Europe     

Zuzana Ďuríčková  Juraj Janák 《Studia Geophysica et Geodaetica》2016,60(4):622-643

The aim of this paper is to evaluate the effects of residual terrain model (RTM) on potential and on gravity and to point out how significant can the omission error of global geopotential models (GGMs) be and how it can influence their testing. The RTM for Central Europe is computed in the spherical approximation. The topography is modelled by spherical tesseroids and the gravitational effect of the topography is obtained as a sum of their partial gravitational effects. A detailed picture of RTM in Slovakia is shown. The testing of GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) global geopotential models in Central Europe published earlier is re-evaluated with the more rigorous omission error estimation. Experimental results show significantly better agreement between the gravity anomalies computed from global geopotential models with the omission-error estimation and gravity anomalies obtained from the direct measurements. On the other hand, for height anomalies such an improvement is not observed. The results are discussed in context of the other previously published studies.  相似文献   

Local spatial nets derived from measurements of angles     

Juraj Šütti  Ján Lehet  Reviewer L. Kubáček 《Studia Geophysica et Geodaetica》1987,31(4):335-343

Summary Some of the properties are discussed of local nets derived from measurements of angles by forward intersection. Their functionals and stochastic model indicate the way the effect of the initial data, of the model of determining refraction conditions can be taken into account, and the possibility of gradually obtaining the individual estimates of the coordinates of the points being determined.

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Accuracy of a free polygonal traverse oriented by gyrotheodolite     

Juraj Šütti 《Studia Geophysica et Geodaetica》1969,13(4):390-399

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Fog Prediction for Road Traffic Safety in a Coastal Desert Region: Improvement of Nowcasting Skills by the Machine-Learning Approach     

Ivana Bartoková  Andreas Bott  Juraj Bartok  Martin Gera 《Boundary-Layer Meteorology》2015,157(3):501-516

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A comprehensive study of distribution laws for the fragments of Košice meteorite     

Maria Gritsevich  Vladimir Vinnikov  Tomáš Kohout  Juraj Tóth  Jouni Peltoniemi  Leonid Turchak  Jenni Virtanen 《Meteoritics & planetary science》2014,49(3):328-345

In this study, we conduct a detailed analysis of the Ko?ice meteorite fall (February 28, 2010), to derive a reliable law describing the mass distribution among the recovered fragments. In total, 218 fragments of the Ko?ice meteorite, with a total mass of 11.285 kg, were analyzed. Bimodal Weibull, bimodal Grady, and bimodal lognormal distributions are found to be the most appropriate for describing the Ko?ice fragmentation process. Based on the assumption of bimodal lognormal, bimodal Grady, bimodal sequential, and bimodal Weibull fragmentation distributions, we suggest that, prior to further extensive fragmentation in the lower atmosphere, the Ko?ice meteoroid was initially represented by two independent pieces with cumulative residual masses of approximately 2 and 9 kg, respectively. The smaller piece produced about 2 kg of multiple lightweight meteorite fragments with the mean around 12 g. The larger one resulted in 9 kg of meteorite fragments, recovered on the ground, including the two heaviest pieces of 2.374 kg and 2.167 kg with the mean around 140 g. Based on our investigations, we conclude that two to three larger fragments of 500–1000 g each should exist, but were either not recovered or not reported by illegal meteorite hunters.  相似文献