Testing for the effects of depositional rates in multiproxy models of environmental and faunal change: the Silurian Lau δ13C excursion

<p>The Silurian is characterized by several extinction events, among them the late Ludfordian Lau event, which mainly affected conodont and graptolite communities. This event was followed by the strongest global positive δ<sup>13</sup>C excursion of the Phanerozoic. This event has been first recognized in the classical succession in Gotland, Sweden, where a continuous increase in δ<sup>13</sup>C values of up to nearly 9 ‰ from the upper När Formation to the Eke Formation is observed. It has been attributed to large scale carbon cycle perturbations. This time period is also characterized by a regression and associated changes in sedimentation and deposition rates. This raises the question to what extent these factors contribute to the observed changes in faunal diversity and geochemical proxies.</p><p>A mechanism linking changes in seawater chemistry and the faunal turnover has been proposed based on a high abundance of malformed acritarchs observed during the onset phase of some Phanerozoic isotope excursions including the Lau isotope excursion. Malformations during the late Silurian Pridoli event coincide with a significant increase in trace metal content measured in fossils and host rock, which suggests the teratology to be caused by metal pollution. However, also in the case on an increase in the trace metal content the contribution of changing depositional rates has not been quantified.  </p><p>Models developed in the field of stratigraphic paleobiology have demonstrated that changing deposition rates have a substantial influence on the stratigraphic distribution of fossils. In the same sense, element concentrations can be altered by changing deposition rates, which may dilute or condense the primary element signal. For this study, concentrations of different trace elements were measured across a profile in an outcrop Bodudd (Gotland) which exposes the Lau isotope excursion from the upper När to the Eke Formation. Using a newly developed statistical method, the effects of changing deposition rates were quantified and the measured element signal corrected for these effects. This method uses a deposition model to transform the measured element signal, which is a function of the stratigraphic height in the outcrop, back into a temporal rate. The temporal rate reflects the primary element signal and is defined as a function of time instead of stratigraphic height. Thus, the effect of changing deposition rates is accounted for. Approximate deposition models were created based on Th concentrations measured across the profile, which act as a proxy for the rate of terrestrial input, and based on the chitinozoan yield, which reflects deposition rates. Pre- and post-transformation element patterns were compared for different deposition models and evaluated with respect to their ability to preserve element peaks.</p>

Precision Analysis of Optical 3D Digitisation of Shaped Elements

This paper presents results of a carried out research in the field of scanning precision of contactless optical 3D scanners. Results stated in this paper bring great benefits to practice, since it demonstrates the quality and limits of measuring by means of contactless optical systems in real conditions and therefore its possible use in the field of inspecting the dimensional and shape precision of industrial products.A measurement etalon of various shapes and sizes was designed and manufactured for the purpose of this analysis. The nominal dimensions of the etalon were set by measuring of the coordinate measuring machine and these real values were compared to the model obtained by optical digitisation of Atos II and RevScan. Based on the evaluation of results, scanner measurement precision diagrams were drawn according to the studied aspects, e.g. dependence on the shape of the measured element and its nominal size. Another essential part of the research was determining the ability of 3D scanners to capture detailed parts of the model and assessing the scanning limits for each of the optical systems.

PIXE MAPS OF INTRACELLULAR ELEMENT DISTRIBUTION IN CEREBELLAR NEURONS

Neurodegenerative disorders are accompanied by altered compositions of metals that may convey some information about the health and possibly metabolic state of neurons. Here we opted for PIXE technique to perform a spatially-resolved elemental analysis of intracellular space of individual neurons. Primarily, we measured element distribution within Purkinje cells (PC) of normal and Lurcher (Lc/+) mutant mice to detect any anomalies in concentrations of individual elements attributable to cell death. Lc/+ mutant mice provide an excellent animal model for time-course of excitotoxic cell death. PCs, some with autofluorescence, were scanned with a proton beam to record their X-ray emission and RBS spectra and to construct 2D-concentration maps of individual elements. PCs with auto-fluorescence, presumed to be either already dead or moribund, showed elevated concentrations of Cu , Fe , and Zn , when compared to healthy PCs. In conclusion, excitotoxic mode of death, as observed in the moribund PCs of Lc/+ cerebellum, may activate enzymatic processes, manifested as increased intracellular concentrations of Cu and Zn that are possibly constituents of some metalloenzyme complexes.

Axis to Plane Perpendicularity Error Evaluation Based on New Generation GPS

In this paper, a method for axis to plane in random direction perpendicularity error evaluation based on new generation GPS is proposed. On the basis of a comprehensive study about the definition and measurement method of perpendicularity error, the evaluation model based on the minimum zone conditions is established. Datum plane is transformed to coordinate plane through transition matrix, so the perpendicularity error of measured element to datum plane can be transformed to that of measured element to coordinate plane. The evaluation model is simplified. Example shows that the perpendicularity error of axis to plane can be evaluated accurately and effectively.

Estimation of wood properties using pin pushing in method with various shapes of the penetration pin

The existing penetration methods for the identification of the density of wood that forms a part of structures do not make it possible to describe the density in the entire element profile but only on its surface. However, wood density changes throughout the profile which affects the accuracy of the density determination. The instruments used until now based on the principle of a pin shot into the material thus needed to be supplemented with a test during which the pin would be pushed at least to the centre of the measured element. Pins of 3 mm in diameter were manufactured with a special jig fastening them to a universal testing machine. Using the testing machine, the force required to push the pin in was measured at a constant travel speed. It has been found out that the mechanical work needed for the pin penetration correlates very well with the wood density determined in the surroundings of the place where the pin was pushed in.