Critical Dynamics of Burst Instabilities in the Portevin-Le Chatelier Effect

We investigate the Portevin-Le Chatelier effect (PLC), by compressing Al-Mg alloys in a very large deformation range, and interpret the results from the viewpoint of phase transitions and critical phenomena. The system undergoes two dynamical phase transitions between intermittent (or "jerky") and "laminar" plastic dynamic phases. Near these two dynamic critical points, the order parameter 1/\tau of the PLC effect exhibits large fluctuations, and "critical slowing down" (i.e., the number $\tau$ of bursts, or plastic instabilities, per unit time slows down considerably).Comment: the published 4-page version is in the PRL web sit

Hydrogen absorption in thin ZnO films prepared by pulsed laser deposition

ZnO films with thickness of ~80 nm were grown by pulsed laser deposition (PLD) on MgO (1 0 0) single crystal and amorphous fused silica (FS) substrates. Structural studies of ZnO films and a high quality reference ZnO single crystal were performed by slow positron implantation spectroscopy (SPIS). It was found that ZnO films exhibit significantly higher density of defects than the reference ZnO crystal. Moreover, the ZnO film deposited on MgO substrate exhibits higher concentration of defects than the film deposited on amorphous FS substrate most probably due to a dense network of misfit dislocations. The ZnO films and the reference ZnO crystal were subsequently loaded with hydrogen by electrochemical cathodic charging. SPIS characterizations revealed that absorbed hydrogen introduces new defects into Zn

Effects of dietary supplementation of nickel and nickel-zinc on femoral bone structure in rabbits

<p>Abstract</p> <p>Background</p> <p>Nickel (Ni) and zinc (Zn) are trace elements present at low concentrations in agroecosystems. Nickel, however, may have toxic effects on living organisms and is often considered as a contaminant. This study reports the effect of peroral administrated Ni or a combination of Ni and Zn on femoral bone structure in rabbits.</p> <p>Methods</p> <p>One month-old female rabbits were divided into three groups of five animals each. Group 1 rabbits were fed a granular feed mixture with addition of 35 g NiCl₂per 100 kg of mixture for 90 days. In group 2, animals were fed a mixture containing 35 g NiCl₂and 30 g ZnCl₂per 100 kg of mixture. Group 3 without administration of additional Ni or Zn served as control. After the 90-day experimental period, femoral length, femoral weight and histological structure of the femur were analyzed and compared.</p> <p>Results</p> <p>The results did not indicate a statistically significant difference in either femoral length or weight between the two experimental groups and the control group. Also, differences in qualitative histological characteristics of the femora among rabbits from the three groups were absent, except for a fewer number of secondary osteons found in the animals of groups 1 and 2. However, values for vascular canal parameters of primary osteons were significantly lower in group 1 than in the control one. Peroral administration of a combination of Ni and Zn (group 2) led to a significant decreased size of the secondary osteons.</p> <p>Conclusions</p> <p>The study indicates that dietary supplementation of Ni (35 g NiCl₂per 100 kg of feed mixture) and Ni-Zn combination (35 g NiCl₂and 30 g ZnCl₂per 100 kg of the mixture) affects the microstructure of compact bone tissue in young rabbits.</p

Applicability of the Photochemically Generated Pendant Benzoyl Peroxides in both “Grafting From” and “Grafting To” Techniques

Methyl methacrylate and styrene copolymers containing pendant benzil groups, such as 1-[4-(2-methacroyloxyethoxy)phenyl]-2-phenyl-1,2-ethanedione-co-methyl metacrylate (BzMA/MMA), 1-[4-(2-methacroyloxyethoxy)phenyl]-2-phenyl-1,2-ethanedione-co-styrene (BzMA/S), and 1-phenyl-2-(4-propenoylphenyl)-1,2-ethanedione-co-styrene (PCOCO/S), were prepared and used as precursors for photochemically generated pendant benzoyl peroxides. Decomposition of the pendant benzoyl peroxides was subsequently used in grafting processes. Either irradiation or a combination of irradiation with subsequent thermal treatment was adopted for grafting a thin layer of BzMA/MMA copolymer onto the surface of LDPE films. The grafting resulted in a significant decrease in contact angle of the film surface. The same activation strategy was successfully adopted to initiate the polymerisation of acrylic or methacrylic acids from the surface of styrene copolymer films containing the initiator precursor in the polymer side chains (BzMA/S and PCOCO/S). The successful surface grafting was proved by contact angles measurement as well as by infrared spectroscopic analysis

Vickers Hardness and Positron Annihilation Study of Eurofer97 and ODS Eurofer

This paper describes investigations of Eurofer97 and oxide dispersion strengthened version of this steel, in as received state and after annealing. Vickers hardness test was performed on the as received specimens and after annealing at various temperatures to obtain information about development of the strength of studied materials. After identifying the temperature region where significant changes of the strength take place we applied positron annihilation spectroscopy to probe the microstructural changes in ferritic/martensitic steels. An observation of phase transformation was observed in both steels at various temperatures indicating different behaviour of the base material and its strengthened version. All applied methods proved the importance of strengthening by oxides to improve properties of steels

Electric properties of anorthite ceramics prepared from illitic clay and oil shale ash

Electrical properties during firing of anorthite ceramic prepared from mixtures of illitic clay (from Northeastern Hungary) and fly ashes (obtained from circulating fluidized bed combustion – IA4 and pulverized firing – ID4) with high content of CaO were investigated. Mixtures were prepared with 60 wt% of illitic clay and 40 wt% of oil shale ash. The ashes were hydrated prior to mixing, to prevent the reaction of free lime with water during sample preparation. The mixtures were subjected to thermal and structural analyses to describe the processes induced by thermal treatment. The contraction of the IA4 and ID4 samples reached 1.8% and 2.5%, respectively, at 1100 °C, which is significantly lower than that of the illitic clay (7%). X-ray diffraction (XRD) analysis revealed a presence of diopside, gehlenite, cristobalite, and leucite minerals as additional mineral phases in the prepared anorthite ceramics. Measurement of AC conductivity showed that after the decomposition of the CaCO3 at ∼880 °C, Ca2+ ions became the dominant charge carriers, and the electrical current was carried by a hopping mechanism throughout the studied temperature region. The electrical conductivity and the relative dielectric constant of the ID4 sample was higher compared to that of the IA4 sample. The relative dielectric constant reached values of 6 (sample IA4) and 8 (sample ID4) at 140 °C (after drying)

Characterization of Defects in Titanium Created by Hydrogen Charging

Hydrogen interaction with vacancies in α-Ti was investigated employing positron lifetime spectroscopy combined with ab initio theoretical modeling of vacancy-hydrogen complexes. Ab initio modeling revealed that multiple hydrogen atoms up to 7 can be trapped at vacancies in the α-Ti lattice. Trapped H atoms are located close to the nearest neighbor tetrahedral sites around the centre of vacancy. Lifetimes of positrons trapped at vacancies associated with various numbers of hydrogen atoms were calculated. Positron lifetime measurement of H-loaded α-Ti samples revealed that phase transition into the hydride phase introduced dislocations. Vacancies were created by H loading as well and agglomerated into small vacancy clusters