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  • Author: Jiří Lukas x
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Reconstruction attempt in the case of the hoard of the deniers dating back to the 10th century found near Ústí nad Labem (Based on hand-written notes by E. Fiala)

Abstract

The article offers a partial reconstruction attempt focused on the hoard of the Bohemian deniers struck under Boleslaus II (972–999) discovered in the surroundings of Ústí nad Labem sometimes before 1895. The reconstruction is based on analysis of older literature and the hand-written notes produced by the Czech numismatist Eduard Fiala.

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New Moravian deniers of the C 301 type struck under Břetislaus I and found at the Vraclav hillfort

Abstract

Two fragments of extraordinarily rare Moravian deniers of the C 301 type struck under Břetislaus I before 1030 were found during archaeological surface examinations at the Vraclav hillfort (Ústí nad Orlicí district, Pardubice region) in 2006–2016. There is the name of Břetislaus without his princely title on obverse, and the name of St. Clement, the Moravian patron, on reverse. Besides the described fragments, only four specimens of this type are known from foreign hoards (finds). Both fragments from the Vraclav hillfort represent the earliest precisely datable proof of penetration of the Moravian coins into the Bohemian territory.

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Design of Grinding Machine Spindle

Abstract

When grinding high demands are usually placed on the geometrical tolerances of the workpiece surface. For this reason, the spindles of the grinding machines are normally designed with requirements for a minimum position change of the grinding disks due to external forces and bending moments. The design theory of these spindles is relatively well elaborated, as it represents the most frequently used solution in practice. However, there are also cases where it is necessary to grind some hard-to-reach areas, using a great ejection of the spindle. In these cases, it is necessary to reassess the required geometrical tolerances with regard to its necessity to comply with the minimal changes in the position of the grinding discs due to the great ejection. Where it is necessary to maintain high geometrical tolerances, it is necessary to ensure a greater rigidity of the spindle. This rigidity is usually improved by increasing its diameter. By doing this we also increase the weight of the spindle that is heavily ejected, and thus its deformation can occur due to gravity forces. That is why it is necessary to analyse the deflection of the spindle depending on its ejection in the course of its design. In the case we increase the diameter of the grinder spindle the possible applicable grinding disc diameter decreases, due to the growing size of its housing. Any grinding of hard-to-reach surfaces is therefore done in particular to improve the quality of the surface with low requirements on the geometrical tolerances. This article deals with the design patterns for a spindle used in axial grinding for inner rotating surfaces. The article contains a spindle design solution and an analysis of its deflections, depending on its ejection, and the size of the passive forces.

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Influences on plasma cutting quality on CNC machine

Abstract

This article discusses plasma cutting technology and its influences on the quality of the resulting cut. Plasma or a plasma arch consists of positive and negatively charged particles, excited and neutral atoms and molecules. As it contains free particles, it is electrically conductive and thus subject to the effects of the electrical and magnetic field. The basis of CNC machine design is described in the article, which has at least 3 axes (x, y, z), but there are also more technologically demanding applications, such as pipe cutting, profile and cutting using chamfer to prepare surfaces for welding, where these multi-axis devices are frequently used. The principle of plasma cutting and the plasma cutting phase is described in this article. The materials that can be divided by a plasma arc are described in detail, including graphs displaying the dependence of sheet thickness on the cutting speed. The article describes and lists the gases that are used in plasma-arc cutting, such as oxygen, argon, hydrogen and nitrogen. Important components of plasma cutting technology are the parameters that can be adjusted and set before the cutting so that the cut is of good quality. The most comprehensive chapter deals with the influences that affect plasma cutting quality. Cutting quality can be influenced by a number of factors. Everything starts with the proper choice of a CNC machine and a plasma source. The quality also depends on the expertise and experience of the machine operator and the setting of the plasma cutting parameters. This issue of influences on the plasma cutting quality is based on long-term experience in the field of the thermal cutting process.

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Mixing system for highly concentrated fine-grained suspensions

Mixing system for highly concentrated fine-grained suspensions

The mixing equipment for highly concentrated fine-grained suspensions must be designed differently from the equipment in which a suspension with a low concentration of the solid phase or bigger particles is mixed. It is due to the different rheological properties of the suspensions. In this work we are trying to find a suitable mixing system for a highly concentrated fine-grained suspension. The aim was to determine an effect of particular geometrical parameters of the tested mixing systems on a suspension process, especially from the energetic viewpoint. The energetic costs of all the used mixing systems were compared on the basis of the power consumption which was necessary for reaching the state of sufficient suspension movement in the whole mixed bulk. As a result, it was confirmed that multistage impellers can be used even in standard vessels (with a liquid level height equal to a vessel diameter) with a profit. During experiments, the state of sufficient movement was determined by a visual observation of the suspension at the vessel bottom, at the wall and also at the suspension level.

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Extinction of Lasiommata petropolitana (Fabricius, 1787) (Lepidoptera: Nymphalidae) in the Czech Republic: a case of habitat loss at a range margin

Abstract

Lasiommata petropolitana is a boreomontane butterfly, declining in Central Europe and not recorded in the Czech Republic since 1975. Based on revision of all existing archival records and results of recent targeted surveys in mountainous regions of East Moravia, area of its past occurrence, we document its gradual retreat and ultimate regional extinction. The historical range, marginal with respect to contiguous distribution along the Carpathian mountain chain, included both foothills and higher elevations of Bílé Karpaty, Hostýnské Vrchy, Javorníky, Moravskoslezské Beskydy and Vsetínské Vrchy Mts; pre-1950 records document also a past occurrence at calcareous bedrock localities in Brno environs. Other past lowland records (Oslava valley, Olomouc, Znojmo) were due to misidentifications. Within the historical Czech range, the butterfly inhabited pastures with exposed calcareous, flysh or sandstone bedrock, maintained by traditional grazing. The decline of the species proceeded from lower elevations and foothills towards mountain ridges. The higher elevation sites were encroached by successional changes, or intentionally afforested, with post-war decline of mountain grazing. This development went largely unnoticed by conservation authorities, and represents a loss of mountain butterfly from marginal parts of its range.

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The effect of CO2 on cement composites produced with an admixture of waste sludge water from a concrete plant

Abstract

This article presents the results of a research dealing with the effect of CO2 on cement composites prepared on the basis of waste sludge water from the concrete plant. The designed formulas R1 and R3 use waste sludge water from the concrete plant as a partial or complete replacement of mixing water in the production of cement composites. The mixing water was replaced by waste sludge water in the amounts of 25%, 50%, 75% and 100%. Laboratory tests that are defined in ČSN EN 1008 standard were performed in order to determine the effect of partial or complete replacement of mixing water. The test specimens were further subjected to the effect of CO2 in the Lamart laboratory chamber, where the effect of CO2 was simulated for the period 50 years. Subsequently, the cement composites were tested for their strength characteristics (tensile flexural strength, compressive strength) and subjected to a mineralogical analysis. The results show that the effect of CO2 will reduce the strength characteristics of the composite compared to the comparative samples.

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The layering of a mountain podzol can strongly affect the distribution of infiltrated water in the soil profile

Abstract

The layering of the soil profile can influence the accumulation of infiltrated water and the way in which subsurface runoff is formed. This paper examines a mountain podzol characterized by clearly developed soil horizons. After these horizons had been identified, distinct soil layers were defined (the eluvial horizon, the spodic horizon (undifferentiated), and weathered bedrock). Saturated hydraulic conductivity (Ks), particle size distribution and bulk density were measured in these layers. A visualization of the distribution of infiltrated water in the podzolic profile was performed using a dye tracer experiment. The accumulation of dyed water and a distinct lateral flow were detected in the eluvial layer. Only limited entry of water into the spodic layer was observed. These effects were caused by changes in soil hydraulic properties (SHP) among the investigated layers. For the spodic horizons, the measured Ks value (crucial SHP) was significantly lower than the Ks values for the other tested horizons. The probable reason for the lower Ks was an accumulation of fine particles and various substances in the spodic horizons, and corresponding changes in the porous system. The observed effects of layering indicate that water can be accumulated and subsurface runoff can be formed over the spodic layer during intensive rain or snow melting.

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Constraints on the origin of gabbroic rocks from the Moldanubian-Moravian units boundary (Bohemian Massif, Czech Republic and Austria)

Constraints on the origin of gabbroic rocks from the Moldanubian-Moravian units boundary (Bohemian Massif, Czech Republic and Austria)

Gabbroic bodies from the Moldanubian Monotonous Group (Maříž) and the Moravian Vratěnín Unit (other sites), often showing retrogressive recrystallization at their margins in the amphibolite-facies grade, have norite, gabbronorite, gabbro and hornblendite compositions. Gabbros with preserved coronitic textures are limited to the Vratěnín Unit. The estimated equilibration temperatures derived from plagioclase-amphibole pairs and orthopyroxene Ca contents calculated for pressures 5-10 kbar overlap for coronitic (700-840 °C) and non-coronitic gabbroic rocks (680-850 °C). Although the Moldanubian (Maříž) gabbroic rocks are more Mg-rich compared to the Moravian gabbroids, they show crust-like La/Nb ratios of 2.1-6.6 characteristic of subduction-related magmatic rocks coupled with uniform low εNd values of + 0.6 to + 0.7. Apparent subduction-related features are probably caused by contamination by juvenile crust and/or by metamorphic fluid rich in incompatible elements during the Variscan metamorphism. Samples from Korolupy-Nonndorf and Mešovice have La/Nb ratios < 1.7 and show negative correlations between La/Nb and εNd. Such decoupling between La/Nb and εNd could be attributed to contamination of the subduction-related parent magma by crustal material with higher La/Nb and lower εNd values. Samples from Uherčice show ambiguous geochemical patterns inherited from contamination by very old recycled material. Gabbroic rocks from Maříž should represent an underplated, partly layered cumulate body of continental tholeiite composition, strongly influenced by crustal contamination. In contrast, gabbroic bodies from the Vratěnín Unit, having a close spatial relationship to the surrounding garnet amphibolites, were emplaced into a lithologically variable passive margin sequence probably during the Cadomian extension.

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Long-term transformation of submontane spruce-beech forests in the Jizerské hory Mts.: dynamics of natural regeneration

Abstract

The paper deals with development of the natural regeneration of even-aged spruce-beech forests during their transformation to uneven-aged stands with diversified structure at the Jedlový důl area in the Protected Landscape Area Jizerské hory Mts., Czech Republic. Shelterwood management system and free felling policy based on selection principles has been applied there since 1979 with the support of admixed tree species of the natural species composition, especially silver fir (Abies alba Mill.). The research was focuses on structure and development of natural regeneration with the emphasis on ungulate damage and interaction with tree layer from 1979 to 2015. In the course of 36 years, the regeneration structure was diversified towards the close-to-nature tree species composition, spatial and age structure. The number of regeneration recruits increased in average from 941 to 41,669 ind ha-1. During this period share of European beech (Fagus sylvatica L.) significantly (p < 0.01) increased (by 53.6%), while the share of Norway spruce (Picea abies [L.] Karst.) decreased (by 51.5%), such as damage caused by ungulate (by 61.4%) with the highest loses on sycamore maple (Acer pseudoplatanus L.), rowan (Sorbus aucuparia L.) and silver fir. Moreover, the parent trees had a significant negative influence on natural regeneration at smaller spacing (within a 1 - 5 m radius from the stem). Both, regeneration potential and effective role of the tree layer during the forest transformation has been confirmed as important prerequisites for ongoing forest transformation.

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