Crystallization behaviour of Al-based amorphous alloy and nanocomposites by rapid quenching

The microstructure and crystallization behaviour of melt-spun Al₈₈Ni₉Ce₂Fe₁ amorphous alloy and nanophase composites have been studied by means of X-ray diffraction, transmission electron microscopy and scanning and isothermal calorimetry. The diffraction patterns from Al₈₈Ni₉Ce₂Fe₁ amorphous alloys are diffuse, indicating a basically amorphous structure but contain two rings presumed to be associated with quenched-in nuclei. In the cases of Al₈₈Ni₉Ce₂Fe₁ nanophase composites, nanoscale precipitated particles are homogeneously dispersed in an amorphous matrix, and the crystallite diameter and volume fraction are sensitive to quenching conditions. During thermal crystallization, a two-step phase transformation occurs in the amorphous alloy and nanocomposites, which is characterized by a diffusion-controlled precipitation of nanoscale Al particles and the growth of a Al₃(Ni, Fe) nanophase prior to a Al₁₁Ce₃ nanophase. This study gives insight into structure-control for obtaining nanophases dispersed in an amorphous matrix by rapid quenching.     

Linear-parabolic shift of initially sharp interface in AB diffusion couple above the ordering temperature

It is shown that initially sharp interface in AB diffusion couple, above the ordering temperature, can shift with anomalous kinetics, i.e. deviations from the parabolic growth kinetics are possible. The initial slopes of the shift versus time functions can be even unity for large diffusion asymmetry (the ratio of diffusion coefficients of the parent materials in orders of magnitude) and gradually decrease to 0.5 at larger distances (longer times). This is in accordance with earlier results obtained in phase separating systems. It is shown that from the results of simulations the crossover thickness, X*, between the linear and parabolic regimes can also be calculated, and the applicability of the linear–parabolic law is confirmed. Furthermore, it is illustrated that the crossover thickness depends exponentially on the diffusion asymmetry parameter, with the exponent close to the value obtained from analytical estimations.     

Specific heat and low-field magnetocaloric effect in A-site ordered PrBaMn2O6 manganite

The specific heat and magnetocaloric effect (MCE) of A-site ordered PrBaMn₂O₆ manganite have been studied. The anomalies caused by the ferromagnetic (FM) and antiferromagnetic (AFM) phase transitions are revealed in the specific heat curve. Direct and inverse MCE are observed at the Curie and Néel points correspondingly. A value of the inverse MCE in the heating run is smaller than in the cooling regime. We attribute this effect to the competition between FM and AFM interactions. A significant advantage of PrBaMn₂O₆ as a magnetocaloric material is an MCE spanning a broad range of temperature with a maximum at room temperature.     

Role of cross-slipping in formation of edge dislocations in heteroepitaxial systems GeSi-on-Si(001) and Ge-on-InGaAs/GaAs

Edge misfit dislocations (MDs) formed as result of reactions between 60° glissile threading dislocations and 60° MDs lying on an intersecting glide plane were found in strained GeSi-on-Si(001) and Ge-on-InGaAs/GaAs films. It was demonstrated that dislocations penetrating from the InGaAs buffer layer to the strained Ge film can provoke formation of not only 60° MDs, but also edge MDs on the interface even at minor mismatch of the lattice parameters of the film and the InGaAs/GaAs virtual substrate.     

Experimental evidence for action imitation in killer whales (Orcinus orca)

Comparative experimental studies of imitative learning have focused mainly on primates and birds. However, cetaceans are promising candidates to display imitative learning as they have evolved in socioecological settings that have selected for large brains, complex sociality, and coordinated predatory tactics. Here we tested imitative learning in killer whales, Orcinus orca. We used a ‘do-as-other-does’ paradigm in which 3 subjects witnessed a conspecific demonstrator’s performance that included 15 familiar and 4 novel behaviours. The three subjects (1) learned the copy command signal ‘Do that’ very quickly, that is, 20 trials on average; (2) copied 100 % of the demonstrator’s familiar and novel actions; (3) achieved full matches in the first attempt for 8–13 familiar behaviours (out of 15) and for the 2 novel behaviours (out of 2) in one subject; and (4) took no longer than 8 trials to accurately copy any familiar behaviour, and no longer than 16 trials to copy any novel behaviour. This study provides experimental evidence for body imitation, including production imitation, in killer whales that is comparable to that observed in dolphins tested under similar conditions. These findings suggest that imitative learning may underpin some of the group-specific traditions reported in killer whales in the field.     

Cue competition effects in the planarian

The learning abilities of planarian worms (Dugesia tigrina) were assessed by using a number of Pavlovian conditioning paradigms. Experiment 1 showed that planaria were susceptible to basic conditioning in that they readily developed a conditioned response to a change in ambient luminance when it was consistently paired with an electric shock over a number of trials. In Experiment 2, the change in luminance was presented in a compound with a vibration stimulus during conditioning. Subsequent tests revealed poor conditioning of the elements compared with control groups in which the animals were conditioned in the presence of the elements alone, an instance of overshadowing. In Experiment 3, pre-training of one of the elements before compound conditioning resulted in blocking of learning about the other element. These results add to other studies that have reported cue competition effects in animal species belonging to different phyla (chordate, mollusk, arthropod), suggesting that learning in these phyla could be ruled by similar principles. The results are discussed adopting an evolutionary-comparative approach.