Despite being known for over 155 years, the Late Cretaceous marine amniotes of the Bohemian Cretaceous Basin in the Czech Republic have received little recent attention. These fossils are however significant because they record a diverse range of taxa from an incompletely known geological interval: the Turonian. The presently identifiable remains include isolated bones and teeth, together with a few disarticulated skeletons. The most productive stratigraphical unit is the Lower–Middle Turonian Bílá Hora Formation, which has yielded small dermochelyoid sea turtles, a possible polycotylid plesiosaur and elements compatible with the giant predatory pliosauromorphPolyptychodon. A huge protostegid, together with an enigmatic cheloniid-like turtle,Polyptychodon-like dentigerous components, an elasmosaurid and a tethysaurine mosasauroid have also been found in strata corresponding to the Middle–Upper Turonian Jizera Formation and Upper Turonian – Coniacian Teplice Formation. The compositional character of the Bohemian Cretaceous Basin fauna is compatible with coeval assemblages from elsewhere along the peri-Tethyan shelf of Europe, and incorporates the globally terminal Middle–Upper Turonian occurrence of pliosauromorph megacarnivores, which were seemingly replaced by mosasauroids later in the Cretaceous.
Seven cystoid taxa, including one new species, are described or re-described from the Třenice and Mílina formations (Lower Ordovician, upper Tremadocian) of the Prague Basin: Macrocystella cf. greylingi, Echinosphaerites concomitans, E. sp., Glyptosphaerites ferrigena, Paleosphaeronites crateriformis, P. grossularia and Pyrocystites sp. New data on the morphology of Paleosphaeronites, i.e., gonoduct canal and palatal plates in peristome, are presented. A fixo-sessile mode of life of Paleosphaeronites is documented by the specimens attached to trilobite exoskeletons. The described cystoid fauna is one of the earliest yet known, and indicates remarkable echinoderm diversity and favourable marine environment in the late Tremadocian in the European part of peri-Gondwana region.•
This paper describes a new non-destructive approach for porosity measurement developed in response to a need for a more accurate porosity measurement method for solid samples. The conventional methods in X-ray CT imaging are based on image segmentation where a threshold is applied at a user-defined value. As a result the uncertainty in the porosity measurement is introduced. Therefore, the new method, called the grey level method, which reflects the phenomenon of image processing and computation of ration between the volume of voids and the total volume of the entire sample, was considered and improved in term of image noise and artifacts. The volumes of 2D CT image as a surface are achieved by means of integrating the surface with operations relating to image histogram. The porosity value is given form the curve of a porosity distribution. Subsequently, the properties of individual pores were measured and comparison with conventional destructive method of porosity computation was carried out. Data analysis and image processing were realized in Matlab.
Computer tomography could be used for non-destructive inspection of castings. This contribution deals with application of computer tomography for determination of inner quality of high-pressure die casting parts, especially in relation to leakage and compared with other testing methods. In praxis, the leakage location is identified by fracture test or by metallographic observation. Often the oxides and porosity are found. Porosity is also often found out after machining operations. This work proposes non-destructive methods of castings inspection, especially tomography, in comparison of other known and available methods, with the goal to find out the problem before machining with minimal losses.
This paper presents the study on the feasibility of a differentiation of the individual materials using so called dual energy computed tomography. The individual pixels on tomogram are the results of X-ray attenuation penetrating through the sample from different angles of projections. Attenuation is caused by absorption and scattering of radiation. The contribution of these two main mechanisms is dependent on atomic number, electron density, and also the energy of the X-ray photons. The material characteristics may be quantitatively analyzed when the composition in to atomic number or density information is carried out. Therefore, two different X-ray spectra were used by application of filters. The principle of proposed method results in a numerical approach with the associated detector calibration. We tested first the method on the samples of known composition. From the results it was shown that we are able to obtain removal of "beam hardening" and the estimation of material composition. For further more precise determination of materials, the proposed method will be used with the respect to detector acquisition improvement.
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