Impact resistance of high-density polyethylene against falling penetrator with different potential energy

This study deals with high-density polyethylene (HDPE) which was subjected the drop-weight test. HDPE is a semicrystalline thermoplastic polymer which is commonly used in many applications and mainly in the automotive industry because of its properties. The injection moulded HDPE samples were subjected the penetration test at different potential energies and the results were subsequently evaluated and discussed. The samples were tested in the range of potential energies from 30 to 230 J. The first sample penetration occurred at the energy 50 J. It was found out that the potential energy 30 J is too small for penetration of this material, which shows the impact resistance of HDPE. © The Authors, published by EDP Sciences, 2017

Influence of fall height on high impact polystyrene deformation and characteristics of drop weight test

This study deals with high impact polystyrene (HIPS) which was subjected the drop-weight test. HIPS is a polymer produced by the reaction between butadiene synthetic elastomer and styrene (5-14 %) which contains the crystal polymer in certain amounts and is commonly used in mechanical engineering applications where machine parts are exposed to impact loading. The injection moulded HIPS samples were subjected the penetration test at different fall heights and the results were subsequently evaluated and discussed. It was found out that all fall heights are suitable for HIPS penetration, but the optimal one is 50 J because of the smallest variation range. Higher heights are not needed because of increasing power consumption of the test device. From the results, it is clear, that HIPS is not so highly impact resistant material as for example HDPE, because of that is this material suitable for applications where is not often exposed to too big impacts at high velocities. © The Authors, published by EDP Sciences, 2017

The rise of Christianity and cities of God : some critical remarks to the works of Rodney Stark

This article tries to highlight some problematic views connected with Rodney Stark's application of "religious market model" in the context of the late antique world. It seems that: 1) Stark's general assessment about the character of the religious market of the Roman empire is incorrect (the market is pluralistic, but not unregulated); 2) his theory does not cover full spectrum of potential producers of religious product (especially producers of collective goods of non-exclusive character); 3) his theory excludes "firms" belonging to the state and city public cults; 4) his statistical evaluations are based on unknown statistical data; 5) there are some opinions in his narrative that appear to be uncritically favoring Christian attitudes and achievements and denigrating the pagan ones, which does not, in my opinion, meet requirements of scientific objectivity and impartiality.This article tries to highlight some problematic views connected with Rodney Stark's application of "religious market model" in the context of the late antique world. It seems that: 1) Stark's general assessment about the character of the religious market of the Roman empire is incorrect (the market is pluralistic, but not unregulated); 2) his theory does not cover full spectrum of potential producers of religious product (especially producers of collective goods of non-exclusive character); 3) his theory excludes "firms" belonging to the state and city public cults; 4) his statistical evaluations are based on unknown statistical data; 5) there are some opinions in his narrative that appear to be uncritically favoring Christian attitudes and achievements and denigrating the pagan ones, which does not, in my opinion, meet requirements of scientific objectivity and impartiality