Microstructural changes upon annealing in ODS-strengthened ultrafine grained ferritic steel

In this study, the stability of grain size and oxide nanoparticles in the ODS steel upon annealing at high temperature (650–1350 °C) has been evaluated. The ODS Fe–Cr–W–Ti–Y₂O₃ steel has been manufactured by powder metallurgy, consolidated by hot isostatic pressing and processed by hydrostatic extrusion. Such a processing brings about ultrafine grain structure reinforced with oxide nanoparticles (few nm in diameter) and results in superior mechanical properties. The stability of nano-oxides has been analyzed by small angle X-ray scattering together with transmission electron microscopy. The results obtained revealed excellent thermal stability of ultrafine grained ODS ferritic steel, which was attributed to the resistance of oxides against coarsening.     

Studying the Mechanical Behaviour of Asphalt Mixture with the Grid Method

Abstract: The aim of this work is to analyse the strain fields that take place in several asphalt mixture specimens subjected to compression tests. The grid technique is used for this purpose. The main features of this strain measurement technique are first described. The obtained results are then discussed. They show that very strong heterogeneities take place in the strain fields. They are due to the very different mechanical properties of the constituents. Various testing conditions are also investigated because they directly influence the quality of the measurements and the ability of the grid technique to detect small strain amplitudes with a good spatial resolution, this last feature being crucial here because of the very nature of the material under test.     

Laser ignition of explosives: Effects of gas pressure on the threshold ignition energy

Abstract

This paper describes a method for measuring the effect of initial gas pressure and the type of gas on the threshold ignition energy of several high explosives. The method is based on a 300 W CW CO₂-laser. An extensive study of these parameters for PETN and RDX is also presented. These high explosives all show a strong decrease in ignition energy/power with increasing initial gas pressure. The gases tested are air and nitrogen. The studied pressures are in the interval 0.1 to 10 MPa. The ignitability of PETN and RDX was tested at a laser pulse width of 1.2 ms. All tested high explosives had a lower ignition energy/power in air than in nitrogen at low pressures (< 2 MPa), whereas RDX and PETN had a lower ignition energy in nitrogen than in air at high pressures (>4 MPa). For TNT the time to ignition, measured as a function of air pressure, decreased with increasing pressure. These results are interpreted as a multiple phase ignition process. The method was also used for obtaining ignition data for TNT, Comp B-3 and Torpex.     

Croatia

Abstract

When we speak about early photography in Yugoslavia, we must bear in mind the geographical and political situation of the country at the time when photography appeared. In the 19th century, Croatia, today one of the six Yugoslav federal republics, was a part of the Austro-Hungarian monarchy. So was Slovenia and, in the latter part of the century, Bosnia and Hercegovina, while Serbia and Montenegro had emerged from the disintegration of the Ottoman empire as small independent states. In this survey we shall consider the beginnings of photography in Croatia, not just because that aspect has been studied the most, but because Croatia's special position within the boundaries of Austria-Hungary led to a correspondingly rapid development of photography in this area, as compared with other Slav lands in the south.     

Electrochemical hydrogen storage in activated carbons with different pore structures derived from certain lignocellulose materials

Activated carbons exhibiting high hydrogen electrosorption were produced from selected precursors: coconut shells, blackthorn stones, cellulose and lignin. The influence of the carbonization condition and activation with KOH on their structural parameters and, hence, hydrogen electrosorption ability, was investigated. A positive effect of fast, aggressive activation was demonstrated for precursors subjected to initial carbonization at moderately high temperature (700 °C). The highest hydrogen electrosorption, allowing storage of electrical charge of 625 mA h g^?1, an equivalent of hydrogen gas storage of 2.31 wt.%, was obtained for blackthorn stones after 15 min activation at 950 °C and carbonizate/KOH ratio of 1/5. Further prolongation of the activation process is disadvantageous as it leads to the burn-off of the sample and the increase of the micropore diameter and, finally, reduction of hydrogen sorption ability. This loss cannot be fully compensated by the secondary pores created afterwards by the burn-off with K₂CO₃. The investigations confirmed that an efficient hydrogen electrosorption could be obtained by using active carbons made of cheap and easily available natural, plant-derived precursors, instead of special carbonaceous materials produced by complicated methods.     

Evaluation of steganographic methods for oversized IP packets

This paper describes new network steganography methods that utilize mechanisms for handling oversized IP packets: IP fragmentation, PMTUD (Path MTU Discovery) and PLPMTUD (Packetization Layer Path MTU Discovery). In particular, for these mechanisms we propose two new steganographic methods and three extensions of existing ones. We present how mentioned mechanisms can be used to enable hidden communication for both versions of IP protocol: 4 and 6 and how they can be detected. Results for experimental evaluation of IP fragmentation steganographic methods are also enclosed in this paper.     

Corrosion resistance of model ultrafine-grained Al–Li alloys produced by severe plastic deformation

The influence of grain boundaries and fine precipitation on the corrosion behavior was investigated in two model aluminum–lithium alloys, namely (in wt%) Al–1.6Li (lithium in a solid solution) and Al–2.3Li (lithium in the form of Al₃Li precipitation), subjected to three different severe plastic deformation (SPD) treatments which refined the microstructure of the alloys to the ultrafine grain size. The SPD techniques used in the experiments were equal channel angular pressing (ECAP), hydrostatic extrusion (HE), and extrusion-torsion (ET). The corrosion behavior was examined using a potentiodynamic polarization test, electrochemical impedance spectroscopy, and an immersion test followed by a SEM surface analysis. The electrochemical tests were conducted in a 0.1 M Na₂SO₄ solution added with 100 ppm of Cl⁻. The immersion tests (48 h) were performed in a 3.5% NaCl solution at room temperature. The results indicate that the pitting potential, pit number, and stability of the passive layer formed on the surface of the substrates undergo changes depending on the average grain size and the presence of precipitation or its lack. The corrosion resistance, examined in the solution mentioned above, appears to increase with decreasing average grain size. The ET method gave the microstructure with the lowest corrosion resistance.     

Characterization of Passive Film Formed on AISI 316L Stainless Steel after Magnetoelectropolishing in a Broad Range of Polarization Parameters

The aim of the paper is to present the changes in the surface film composition on AISI 316L stainless steel (SS) after electropolishing (EP) and magnetoelectropolishing (MEP) in a broad range of the process conditions. The X‐ray photoelectron spectroscopy surface analyses were performed to reveal the effect of MEP. The EP process has been performed under natural convection (in a stagnant electrolyte), much above the polarization plateau. A series of experiments were carried out on AISI 316L SS samples in accordance with the five‐level composite rotary statistical plan with the variables being the magnetic field intensity B (mT), and the anodic current density i (A dm^?2). XP high resolution spectra have been obtained on AISI 316L SS surface concerning Fe 2p, Cr 2p, O 1s, S 2p, P 2p, and C 1s, respectively. The Cr:Fe ratio regarding both metallic M and compound X was also studied and calculated. At the end, the summary results of Cr/Fe = f(B, i) in relation to the corrosion potential, have been compared. The conclusions, concerning the selection of MEP process conditions, regarding the optimum Cr/Fe ratio and corrosion behavior, have been formulated. It was found the Cr:Fe ratio well correlates with the pitting corrosion potential. MEP process can modify not only the rate of dissolution to a determined extent, but also control the corrosion behavior and Cr:Fe ratio results.     

Replication of an experiment on linguistic tool support for consolidation of requirements from multiple sources

Large market-driven software companies continuously receive large numbers of requirements and change requests from multiple sources. The task of analyzing those requests against each other and against already analyzed or implemented functionality then recording similarities between them, also called the requirements consolidation task, may be challenging and time consuming. This paper presents a replicated experiment designed to further investigate the linguistic tool support for the requirements consolidation task. In this replication study, 45 subjects, working in pairs on the same set of requirements as in the original study, were assigned to use two methods for the requirements consolidation: (1) lexical similarity and (2) searching and filtering. The results show that the linguistic method used in this experiment is not more efficient in consolidating requirements than the searching and filtering method, which contradicts the findings of the original study. However, we confirm the previous results that the assisted method (lexical similarity) can deliver more correct links and miss fewer links than the manual method (searching and filtering).