Directional Distribution of Observable Comets Induced by A Star Passage Through the Oort Cloud

We simulated the passage of a star through the Oort cometary cloud andanalyzed the resulting sample of observable long period comets, noting strong asymmetries in the directional distribution of the perihelion points of thosecomets. We discuss the results previously published byWeissman (1996) for the same case. An explanation is suggestedwhy the isotropic output can be obtained only for a very peculiar case. The``cometary shower' density variation with time is also presented and thetime-dependence of the directional distribution is discussed.     

A facies geological test of stable isotope interpretation of the Upper Permian depositional environment in West Spitsbergen

Lithofacies analysis of two transgressive sequences within the Kapp Starostin Formation (Upper Permian, West Spitsbergen), indicates considerable differences in seawater chemistry between their depositional environments. The onshore part of the sequence represented in the Vøringen and Svenskeegga Members is largely calcareous, with allochthonous and corroded siliceous materials. In contrast, in the equivalent sequence within the Hovtinden Member, silica is ubiquitous whereas carbonate materials include mainly corroded bioclasts. These differences are consistent with predictions of the oceanographic model of ‘overfed’ and ‘hungry’ oceans proposed previously on the basis of carbon and oxygen stable isotope analysis.     

Impact Break-Up of Cometary Nuclei – Conclusions from Impact Experiments

Experiments of impact-generated break-up of icy and icy/mineral targets were performed. Formulae for the velocity of ejecta and for energy of disruption were fitted to the experimental data. An assumption that these formulae can be extrapolated for kilometer-size bodies enabled us to discuss the consequences of impacts on cometary nuclei and on planetesimals. It was found that the porosity of the targets as well as their composition (mineral to total mass ratio), are the crucial parameters.     

ChemiX: a Bragg crystal spectrometer for the <Emphasis Type="Italic">Interhelioprobe</Emphasis> interplanetary mission

Interhelioprobe (IHP), an analogue to the ESA Solar Orbiter, is the prospective Russian space solar observatory intended for in-situ and remote sensing investigations of the Sun and the inner heliosphere from a heliocentric orbit with the perihelion of about 60 solar radii. One of several instruments on board will be the Bragg crystal spectrometer ChemiX which will measure X-ray spectra from solar corona structures. Analysis of the spectra will allow the determination of the elemental composition of plasma in hot coronal sources like flares and active regions. ChemiX is under development at the Wroc?aw Solar Physics Division of the Polish Academy of Sciences Space Research Centre in collaboration with an international team (see the co-author list). This paper gives an overview of the ChemiX scientific goals and design preparatory to phase B of the instrument development.     

Observations of the Ly-α Forest

We analyze four high resolution rich samples of Ly-α and metal lines (two at z ≥ 2 and two at z ≤ 0.2). We describe evolution of the observed Doppler parameters and absorbers separation and propose a model of the forest. We argue that all absorption lines are formed in gaseous caustics created in stable DM subclouds. The absorption lines are described by two local characteristics, the Doppler parameter and the column density of neutral hydrogen. We show that evolution of the Doppler parameter is very slow and its mean value increases by a factor ≤1.5 at redshifts 0 ≤ z ≤ 3. We show that absorbers separation increases as <d_sep ∝ (1 + z)?2. We describe evolution of absorbers in the framework of a two component model: the first population represents absorbers with just one line created in compact stable DM clouds with random spatial distribution, and the second population includes absorbers with two, three and more absorption lines formed in more massive and extended random DM clouds. Slow evolution of the Doppler parameter indicates high stability of caustics and conditions within clouds. For absorbers of the second population relative velocity of lines slowly increases with time.     

Multiphase magmatic activity in the Variscan Kłodzko–Złoty Stok intrusion,Polish Sudetes: evidence from SHRIMP U–Pb zircon ages

International Journal of Earth Sciences - The Kłodzko–Złoty Stok intrusion (KZSI), located in the NE part of the Bohemian Massif of Central Europe, has preserved records of the...     

Mixed integer–real least squares estimation for precise GNSS positioning using a modified ambiguity function approach

Mixed integer–real least squares (MIRLS) estimation still has two open scientific problems, i.e., the validation of results and computational efficiency for a large number of satellites. This paper presents and discusses a non-conventional approach to MIRLS estimation, which belongs to the ambiguity function method (AFM) class. Because the solution is searched for in the constant three-dimensional coordinate domain instead of the n-dimensional ambiguity domain, the computational efficiency does not depend as much on the number of satellites as it does in conventional MIRLS estimation. Simple numerical pretests have shown that the reliability and precision of results from the presented approach and the conventional MIRLS estimation are exactly the same. Hence, the presented approach, contrary to AFM, may be treated as MIRLS estimation. Furthermore, the presented approach is a few hundred times faster than AFM and may be considered in (near) real-time GNSS positioning. In light of the above, the new field of research on MIRLS estimation may be opened.