Rock brittleness is one of the most important issues in rock mechanics. There is not yet an available method for defining or measuring directly the rock brittleness. The aim of this study is to suggest a new chemical index parameter for the prediction of basaltic rocks’ brittleness. In the order of that abovementioned purpose, a total of 23 basaltic rock samples were collected from different region of Turkey. Samples were initially tested to determine their chemical properties. Then, mechanical tests were carried out to define the brittleness indices (B1, B2, and B3) for each corresponding sample. Finally, relations between parameters obtained from test results and brittleness indices were examined with regression analysis. According to the results obtained, a new chemical parameter (CP) was proposed for predicting brittleness via major oxide element components of basaltic rocks. It was found out that, B1 and B2 are not reliable parameters for predicting the different properties, however; B3 and CP can be employed as good criteria for predicting the different properties of basaltic rocks (especially in terms of chemical and mechanical properties)., Candan Bilen, Selman Er, Atiye Tuğrul and Murat Yilmaz., and Obsahuje bibliografii
The study focuses on the early medieval large glass beads from the area of Poland, i.e. specimens whose diameter equals at least 1.5 cm but usually ca. 2 cm or more. The main aim of this study is to define their function, considering precise context of discovery of particular specimens, metric data and microscopic analyses. Another important task of the study is to determine whether large beads were local products or imports, and from which region and in what social circumstances they reached the studied area. Alongside macroscopic and stylistic features, chemical composition of glass that was used for production of the beads can be conclusive in this situation. In our opinion, it is a special category of finds that appeared in this part of Europe during the time of cultural and political transformation in the 11th–13th centuries. and Předmětem studie jsou polské nálezy raně středověkých velkých skleněných korálů, tj. exemplářů, jejichž průměr činí nejméně 1,5 cm, ale obvykle kolem 2 cm či více. Hlavním cílem je přispět k objasnění jejich funkce na základě nálezového kontextu, metriky a výsledků mikroskopické analýzy. Neméně důležité jsou otázky, zda se jedná o místní produkci či o importy, jaká je jejich geografická distribuce a sociální charakteristika prostředí, ve kterém byly nalezeny. Kromě makroskopicky patrných a morfologických znaků autorky hodnotí též chemické složení korálů. Docházejí k závěru, že velké korály reprezentují samostatnou kategorii nálezů a jejich výskyt odráží kulturní a politické proměny středoevropské společnosti v 11.–13. století.
Spring wheat plants were grown in pots at three CO2 concentrations (350, 550 and 700 ppm) and three soil water levels (40, 60 and 80% of field water capacity) in field open top chambers and were infested with bird cherry-oat aphids (Rhopalosiphum padi Linnaeus). Aphid population dynamics were recorded throughout the growing season and analysis of the chemical composition of spring wheat leaves was conducted at the same time. Results showed that: (1) Aphid populations increased with raised atmospheric CO2 concentrations. (2) The aphid populations showed different responses to different CO2 concentrations. The population size, population growth rate and population density found under the 350 ppm CO2 treatment was far less than those recorded under the 550 and 700 ppm CO2 treatments. The population size, population growth rate and population density recorded under the 700 ppm CO2 treatment was slightly higher than those recorded under the 550 ppm CO2 treatment. (3) The effect of CO2 concentration on the aphid population was correlated with soil water level. The highest aphid population size was achieved under the 60% soil water treatment. (4) Atmospheric CO2 and soil moisture had significant effects on the chemical composition of the wheat leaves. (5) Aphid population size correlated positively with the concentration of leaf water content, soluble proteins, soluble carbohydrates and starch, while correlating negatively with the concentration of DIMBOA and tannin.
Three different metakaolins processed by a Portuguese factory were studied aiming to assess the influence of chemical and mineralogical composition of metakaolin on mortar characteristics. Mineralogical analysis of both the fine and clay fractions was carried out by X-ray diffraction. Chemical composition (major elements) was analyzed by X-ray fluorescence. Mineralogical composition reveals some significant differences between the studied samples, in both analyzed fractions, metakaolin 2 being richer in kaolinitic minerals. From a chemical point of view, siliceous content is always high (aroun d 60 %) as well as Al2O3 content (around 30 %); once again metakaolin 2 is the one richer in Al2O3 and poorer in sodium and potassium. Metakaolin from the three different batches was incorporated in lime mortars in order to produce a pozzolanic reaction and hence enable them to harden in high relative humidity conditions or, when access to CO2 is limited, as in the case of mortars supporting glazed tiles. Mortars with the same volum etric ratio were tested for flexural and compressive strength at ages of 28 and 90 days, and the module of elasticity was dete rmined. A relation between the mechanical strength achieved by lime mortars with the addition of metakaolin from different batches and metakaolin mineral and chemical composition was assessed. The knowledge of the influence of the metakaolin com position on the strength of the mortars is an important step in improving their performance and extending their application., Ana Luisa Velosa, Fernando Rocha and Rosário Veiga., and Obsahuje bibliografické odkazy