Ion beam deposition of amorphous hydrogenated carbon films on amorphous silicon interlayer: Experiment and simulation

A thick layer of amorphous silicon (a-Si) was deposited on industrial grade crystalline n-Si < 111 > substrate by means of electron beam evaporation. On top of a-Si layer, amorphous hydrogenated carbon (a-C:H) film was grown by direct ion beam deposition from acetylene precursor gas. In order to study on atomic level the a-C:H film growth on amorphous silicon, a theoretical model was developed in a form of reaction rate (kinetic) equations. Numerical simulation using this model has revealed that the ratio of sp³/sp² content in the film is heavily influenced by relaxation rate of the carbon atoms in a sub-surface region of the film that were activated by ion irradiation. The final structure of a-C:H film does not depend much on elemental composition and structure of amorphous Si coating, provided that deposition procedure is not terminated at its initial stage but continues for more than 60 s. It became evident, therefore, that the use of a-Si interlayer with a-C:H films could be particularly beneficial when a need arises to minimize or eliminate the effect of the substrate. As one of such cases, a poor adhesion of amorphous carbon on steel and other ferrous alloys could be mentioned.     

Constraints on great apes' imitation: Model and action selectivity in rehabilitant orangutan (Pongo pygmaeus) imitation.

We discuss selectivity in great ape imitation, on the basis of an observational study of spontaneous imitation in free-ranging rehabilitant orangutans (Pongo pygmaeus). Research on great ape imitation has neglected selectivity, although comparative evidence suggests it may be important. We observed orangutans in central Indonesian Borneo and assessed patterns in the models and actions they spontaneously imitated. The patterns we found resembled those reported in humans. Orangutans preferred models with whom they had positive affective relationships (e.g., important caregiver or older sibling) and actions that reflected their current competence, were receptively familiar, and were relevant to tasks that faced them. Both developmental and individual variability were found. We discuss the probable functions of imitation for great apes and the role of selectivity in directing it. We also make suggestions for more effective elicitation of imitation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Study of the oxygen diffusion on three-way catalysts: a kinetic model

Topics in Catalysis - A computer model was developed to take into account all the phenomena that can occur in 18O/16O isotopic exchange over Pt/CeZrO x materials: adsorption/desorption on the...     

Magnetic resonance spectroscopy for assessing myocardial rejection in the transplanted rat heart

Tandem duplication of a mitochondrial import leader sequence has been shown to markedly increase the efficiency of translocation of chimaeric precursors across mitochondrial membranes to the mitochondrial matrix. The principle of leader sequence duplication was applied to the protein secretion system of the yeast Saccharomyces cerevisiae and of Bacillus subtilis. The secretion signal sequences of yeast invertase and B. subtilis neutral protease were used to direct the secretion of human interferon alpha 4. Our results show that the duplication of these N-terminal signal sequences does not enhance secretion of interferon alpha 4 in either of the cell systems studied.     

Rape in non-human animals: An evolutionary perspective.

Rape-like behaviour has been documented in a number of species of animals. The purpose of this paper is to explain the evolutionary perspective on this behaviour. Several key concepts of modern evolutionary theory are first explained. Then the problem of defining rape in such a way that it is amenable to scientific study is discussed. Agonistic mating, altruistic mating, forced mating, and detrimental mating are defined in terms of costs and benefits to both male and female fitness. The introductory section concludes with a discussion of the role of genes in determining sexual behaviour and the nature of biological adaptations. Forced mating in orangutans, mallard ducks, and scorpionflies is described. The evolution of this behaviour is explained in terms of parental investment and sexual selection theory. Speculations on mechanisms that females might evolve to deal with this coercive male reproductive strategy conclude the paper. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modeling of nitrogen penetration in polycrystalline AISI 316L austenitic stainless steel during plasma nitriding

The nitrogen depth profile in polycrystalline AISI 316L austenitic stainless steel after plasma nitriding at temperatures around 400 °C is analyzed by the “trapping-detrapping” model. This model considers the diffusion of nitrogen under the influence of trap sites formed by local chromium atoms. Nitrogen depth profiles in polycrystalline AISI 316L steel simulated on the basis of this model are in good agreement with experimental nitrogen profiles. The enhanced nitrogen diffusivity as well as a plateau-type shape of nitrogen depth profile can be explained. The nitrogen diffusion coefficient at 400 °C is found to be D = 4.81 × 10⁻¹² cm²/s and the diffusion pre-exponential factor D₀ (0.837 × 10⁻³ cm²/s) and detrapping activation energy E_B (0.28 eV) were deduced from fitting experimental data. It is known that the nitrogen penetration depth (and nitrogen diffusivity) depends on the crystalline orientation and a tentative to take into account this anisotropy effect and describe nitrogen depth profiles in polycrystalline AISI 316L steel is proposed by using different diffusion coefficients characteristic for each crystallite orientation.     

Imitation in free-ranging rehabilitant orangutans (Pongo pygmaeus).

Made an observational study of spontaneous imitation in orangutans (Pongo pygmaeus). Previous studies may have underestimated great apes' imitative capacities by studying Ss under inhibiting conditions. Ss living in enriched environments (i.e., rehabilitation) were used. A sample of spontaneous imitations was collected, and the most complex incidents were analyzed for the likelihood that true imitation, learning new actions by observing rather than by doing, was involved in their acquisition. From 395 hrs of observation and other reports on 26 orangutans, 354 incidents of imitation were identified. Of these, 54 complex incidents were difficult to explain by forms of imitation based on associative processes grounded in experimental learning alone; they were, however, congruent with acquisition processes that include true imitation. These findings suggest that orangutans may be capable of true imitation and point to critical eliciting factors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stress induced and concentration dependent diffusion of nitrogen in plasma nitrided austenitic stainless steel

The nitrogen transport mechanism in austenitic stainless steel during plasma nitriding at moderate temperatures (around 400 °C) is considered by stress induced diffusion model. The model involves diffusion of nitrogen in presence of internal stresses gradient induced by penetrating nitrogen as the next driving force of diffusion after concentration gradient. Furthermore, in the present work it was found that nitrogen diffusion coefficient vary with nitrogen concentration according to well-known Einstein-Smoluchowski relation D(C_N) = f(1/C_N). Nitrogen depth profiles in nitided AISI 316L steel at T = 400 °C for 1, 3 and 8 h calculated on the basis of this model are in good agreement with experimental nitrogen profiles. The dependencies of nitrogen flux and nitriding time on nitrogen concentration, nitrogen surface concentration and penetration depth are analyzed by proposed model. It is shown that, with the increase of nitriding time the compositionally-induced stresses and thickness of stressed steel layer increases.     

Kinetic modeling of laser annealing processes in a-C:H films

In this research work, a nanosecond-pulsed YAG:Nd laser was used to modify the properties of an amorphous hydrogenated carbon film, which was deposited on c-Si substrate. Experimental examination has revealed that the primary effect of irradiation is diamond-to-graphite transformation or, more specifically, carbon sp³-to-sp² hybridization transition. These findings were qualitatively verified by numerical simulation of kinetic processes that proceed in the film under laser irradiation.