In this paper, sandstones from three Czech localities were subjected to mechanical fracture tests in order to obtain their properties. Carboniferous sandstone from the Staříč site was primarily different from the two other Cretaceous sandstones from Podhorní Újezd and Javorka localities in the type of grain contact, as well as in their mineralogical composition of the rock matrix and cement. These differences were primarily reflected in different rock porosities. An advanced assessment of the fracture response of the chevron notch specimens made of sandstones subjected to three-point bending test was carried out by means of the GTDiPS program suggested for processing the loading diagrams. Bending Young's modulus, mode I fracture toughness, and fracture energy were subsequently calculated for all tested sandstone samples. Obtained outcomes show that the sandstone from the Staříč mine exhibits several times higher values of investigated properties than the Podhorní Újezd and Javorka sandstones. This was a result of a higher degree of rock compaction, siliciferous rock cement and, therefore, relatively low total porosity. Internal rock texture and mineralogical composition of matrix or cement are thus one of the most important factors influencing the values of mechanical fracture parameters of sandstones.
The study of the mechanical properties of frozen rock is a basic problem that humans have to face in artificial low-temperature rock engineering and cold region rock engineering. There are few literatures on the dynamic constitutive models of frozen rocks under low-temperature gradients at home and abroad. In this paper, the constitutive model of water-saturated marble under the coupling effects of uniaxial impact compressive load and low-temperature is studied by theoretical analysis and experimental verification. Based on the theory of mechanical element combination, a rock constitutive model considering strain rate effect, damage softening effect and low-temperature effect is established, and the model parameters are determined by fitting method. The dynamic stress-strain curve of water-saturated marble at -30 °Cis predicted. The predicted results are in good agreement with the experimental results and the concordance correlation coefficient is 0.984092. The relevant results of this paper can provide a theoretical reference for the excavation and protection of rock engineering under negative temperature., Junzhe Li, Guang Zhang, Mingze Liu, Shaohua Hu and Xinlong Zhou., and Obsahuje bibliografii
In the introduction, a brief historical overwiev is given if the development of accelerators in the world, with a special emphasis on those, which have found applications in our country. Electrostatic linear acceleratiors like Cockroft-Walton, Van de Graaff, Dynamitron, Tandetron, and so on, are discussed first, followed by high-frequency linear accelerators for radiation technologies, defectoscopy and radiotherapy., Úvodem podáváme krátký pohled na celosvětový vývoj urychlovačů částic. Pozornost je věnována především těm typům, které našly uplatnění u nás. Postupně jsou pak probrány lineární elektrostatické urychlovače, jako Cockroftův-Waltonův a Van de Graaffův generátor, Dynamitron, Tandetron aj. Následují lineární vysokofrekvenční urychlovače pro radiační technologie, defektoskopii a radioterapii., Igor Janovský, Čestmíir Šimáně., and Obsahuje seznam literatury
Let $F=F^{(A,H,t)}$ and $F^1=F^{(A^1,H^1,t^1)}$ be fiber product preserving bundle functors on the category $\mathcal {FM}_m$ of fibred manifolds $Y$ with $m$-dimensional bases and fibred maps covering local diffeomorphisms. We define a quasi-morphism $(A,H,t)\to (A^1,H^1,t^1)$ to be a $GL(m)$-invariant algebra homomorphism $\nu \colon A\to A^1$ with $t^1=\nu \circ t$. The main result is that there exists an $\mathcal {FM}_m$-natural transformation $FY\to F^1Y$ depending on a classical linear connection on the base of $Y$ if and only if there exists a quasi-morphism $(A,H,t)\to (A^1,H^1,t^1)$. As applications, we study existence problems of symmetrization (holonomization) of higher order jets and of holonomic prolongation of general connections.
Firstly, this article outlines the main points made by Peter Winch in his breakthrough book The Idea of a Social Science. Its Fundamentals thesis, inspired by Wittgenstein and his accounts on the relation between language and reality, is the assumption that social sciences engage in philosophical endeavor, because the problems they deal with are not empirical, but conceptual. Following Wittgensteinian line of thought he comes up with the idea that all social action can be explained as rule following and therefore it should be approached by conceptual means other than those used by natural sciences. Secondly, this article explores the impact that The Idea of a Social Science had on the discussion about the nature of social sciences. It outlines it‘s main critiques which deal with (1) Winch’s conception of philosophy (2) the notion of rule following and (3) descriptive nature of Winch‘s approach. Finally, Winch‘s critique of positivism in social sciences is identified as his main and lasting contribution to social thought., Tomáš Dvořák., and Obsahuje bibliografii