Ab initio study of phase transformations in transition-metal disilicides

We suggest and investigate three possible displacive structural transformation paths between the ideal C11_b, C40 and C54 structures in MoSi₂, VSi₂ and TiSi₂. They involve shifts of the (110) atomic planes in the C11_b structure, (0001) planes in the C40 structure and (001) planes in the C54 structure. These planes are shifted in the directions experimentally observed as slip directions during plastic deformation. An analysis of ab initio calculated total energies in MoSi₂, VSi₂ and TiSi₂ along these transformation paths is presented. Since the transition-metal and Si atoms come close together during proposed transformations, and, consequently, the energy barriers between individual structures are high, the estimated transition temperatures are comparable with the melting temperatures of the disilicides studied. This confirms their high thermal stability and indicates that if a phase transformation between C11_b, C40 and C54 structures of the disilicides takes place, then its prevailing mechanism should be diffusional rather than martensitic like. During the transformations studied, atoms come as close together as, for example, in configurations of interstitials. Hence, the present ab initio results can also be employed in fitting adjustable parameters of semi-empirical interatomic potentials for the transition-metal disilicides, in particular of the repulsion at short separations of atoms.     

Influence of different coffee drink preparations on ochratoxin A content and evaluation of the antioxidant activity and caffeine variations

Coffee is one of the most frequently consumed beverages in North America and Europe. It is well known that coffee contains caffeine and that coffee beans can be contaminated by Ochratoxin A (OTA). The operating conditions however affect OTA and caffeine extraction from the roasted coffee. OTA content found in the beverages can be greater than that found in the roasted coffee used to prepare it, representing a potential OTA related risk factor for the human health. Moreover the coffee beans and coffee based beverages have an anti oxidant activity. This study investigates the OTA content, the amount of caffeine, and the antioxidant activity in five different preparations: American coffee, Moka, Italian Espresso, Neapolitan and Turkish coffee. Artificially OTA spiked samples were prepared using artificially contaminated roasted coffee beans. High Pressure Liquid Chromatography with fluorimetric detector was used (LC-FLD). The OTA amount, in all preparations, was 85% lower then the spiking level. Quantitative analysis of the caffeine content in the five coffee preparations was determined by spectrophotometry, and the antioxidant lipophilic and hydrophilic activities of the different coffee preparations were investigated and compared. The caffeine content was directly related to its antioxidant activity; no relation was found between OTA, antioxidant activity and caffeine.     

Characterisation of the exopolysaccharide kefiran produced by lactic acid bacteria entrapped within natural kefir grains

The main goal of this work was to characterise and quantify the exopolysaccharide kefiran and to discover an effective procedure for its isolation from kefir grains, originating from the Caucasian Mountains. Capillary electrophoresis was used for the characterisation and quantification of the d ‐glucose and d ‐galactose in our samples at a mass ratio of 1:0.7. The effect of fermentation time on growth of kefir grains and the content of kefiran within the grains were determined. The pH profiles were monitored dynamically. In addition, the influence of fermentation temperature on kefir grains mass concentration (γ_KG) and the content of kefiran within the grains (w_KEF/KG) were studied. The highest values for both were obtained at 30 °C.     

Evaluation of the phytomass source for composite preparation

The properties of lignocellulose materials from the trunk and bark of trees, and from agricultural sources were investigated by thermogravimetry (TG) and pyrolysis–gas chromatography/mass spectrometry (Py‐GC/MS). The goal was to learn which of the phytomass sources is the most accessible to dehydration and aldol reactions, and in this way could be considered suitable for composite preparation by the thermal pressing treatment. The bagasse second differential thermal analysis peak in air is at the highest temperature acceptable for intermolecular dehydration/crosslinking, and therefore we consider bagasse to be the most suitable candidate for composite preparation. From the TG results in air at 250°C, it follows that willow wood and bagasse are the most thermally resistant sources. The data obtained by Py‐GC/MS analysis showed glycolaldehyde and acetic acid as dominant markers related to adhesion properties via aldol condensation. The detected sum amount of glyceraldehyde and acetic acid decreases in the order: beech wood > bagasse > acacia wood > sugar beet pulp, whereas the remaining species produced much less of it. By comparing results run at above conditions with composite preparation using the pressing thermal treatment at a temperature of 150°C and pressures up to 800 kPa, the suggested evaluation was examined for application on sugar beet residue. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

XRD Analysis of Local Strain Fields in Pearlitic Steels ‐ towards the Fast Examination of Microstructure after Hot Rolling

Analysis of the crystallographic anisotropy of the lattice strains, i.e. the analysis of the dependence of the lattice strain on the crystallographic direction, is discussed to be an efficient method for getting information about the mesoscopic local strains and microscopic local strain fields in dual‐phase materials. This technique is illustrated on the example of hot‐rolled pearlitic steels containing ferritic lamellae separated by cementite from each other. In these samples, the information about the local strain fields was further used to build a microstructure model that describes the interaction between crystallites of different phases on the microscopic scale. Such a microstructure model is quite appropriate for examination of the correlations between the structure and properties of the pearlitic steels, because it links the microstructure parameters obtained using X‐ray diffraction on the atomic level with the interaction between the crystallites or grains of different phases, which can more directly be related to the macroscopic mechanical properties of the materials. The second important result of this study was the detection and explanation of several correlations between individual microstructure parameters, which are obtained from X‐ray diffraction. This offers a possibility to use the X‐ray diffraction for a fast microstructure analysis of pearlitic steels, or generally for a fast microstructure analysis of dual‐phase steels, after or even during the rolling processes.     

Stochastic investigations of pseudo-random number generators

In the process of evaluation and ranking of pseudo-random number generators with assumed uniform distribution U[0, 1), we apply thesequential g-transformation discussed in the author's preceding paper [1]. Thus, the obtained discrete distribution named e(g) may immediately serve for investigations of local properties of pseudo-random sequences. The global properties of these sequences may be estimated by means of severalquality statistics based on the e(g)-distribution. Extensive experiences with the quality statistics lead to the introduction of two numerical estimates of a generator, calledquality andstability. These may serve for global ranking of generators. The developed methods are illustrated on numerous known and new generators.     

Assessment of the residual life of a pipeline bend by metallographic measurements of cavitation damage—Determination of the A-parameter

The residual service life of the components of power plants under conditions of creep can be measured by various methods. As a rule, these methods can be classified as destructive, nondestructive, or analytical. The nondestructive method is based on the determination of the metallographic A-parameter, i.e., a quantity equal to the ratio of the number of damaged grain boundaries to the total number of boundaries in the direction of the principal normal stress. By using this method, we determine the residual service life of a pipeline bend operating at a temperature of 530°C under a stress of 100 MPa.Published in Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 5, pp. 65–72, September–October, 1994.     

Formation of scawtite from mixtures of CaO,dolomite and quartz under hydrothermal conditions

Water suspension of mixtures of CaO, and quartz (CaO/SiO₂ = 1,2; 1,6 and 2,0) in which 10–50 wt % CaO were substituted by dolomite, were hydrothermally treated at 200°C. X-ray phase analysis of reaction products showed that chiefly scawtite and partly calcium- and magnesium silicate hydrates were formed. The scanning electron micrographs showed variations in morphology of scawtite particles in dependence on the molar ratio of CaO/SiO₂.     

The DataGrid Workload Management System: Challenges and Results

The workload management task of the DataGrid project was mandated to define and implement a suitable architecture for distributed scheduling and resource management in a Grid environment. The result was the design and implementation of a Grid Workload Management System, a super-scheduler with the distinguishing property of being able to take data access requirements into account when scheduling jobs to the available Grid resources. Many novel issues in various fields were faced such as resource management, resource reservation and co-allocation, Grid accounting. In this paper, the architecture and the functionality provided by the DataGrid Workload Management System are presented.