Effects of anisotropy on the equilibrium shape of nanoscale pores at grain boundaries

Molecular dynamics simulations have been performed to study the interaction between a faceted pore and an anisotropic grain boundary (GB). Nickel was chosen as a convenient model system. In order to establish the equilibrium crystal shape (ECS) of the pore, studies were also conducted on isolated pores. Isolated pores were found to be subject to the nucleation inhibition of equilibration that has been predicted by Rohrer et al. (J Am Ceram Soc 2000;83:214, 2001;84: 2099). This work shows that configurations close to the ECS can be obtained if supersaturation within a pore is artificially increased by adding mobile adatoms to the internal surfaces of the pores. In the case of pores located at GBs, the nucleation energy barriers to facet displacement are not present for facets in contact with the GB at the triple line, but may still persist for facets that have no contact with the GB. This problem can be overcome by approaching the equilibrium shape from different initial configurations. The configuration of the GB in the vicinity of the pore has been found to be essentially planar, indicating that GB puckering in the vicinity of anisotropic pores is not generally necessary. The present calculations show that incompatibilities between misoriented pore facets that meet at the triple line with the GB are easily accommodated by local atomic rearrangements at the disordered region of intersection with the GB

Prewetting transition on a weakly disordered substrate : evidence for a creeping film dynamics

We present the first microscopic images of the prewetting transition of a liquid film on a solid surface. Pictures of the local coverage map of a helium film on a cesium metal surface are taken while the temperature is raised through the transition. The film edge is found to advance at constant temperature by successive avalanches in a creep motion with a macroscopic correlation length. The creep velocity varies strongly in a narrow temperature range. The retreat motion is obtained only at much lower temperature, conforming to the strong hysteresis observed for prewetting transition on a disordered surface. Prewetting transition on such disordered surfaces appears to give rise to dynamical phenomena similar to what is observed for domain wall motions in 2D magnets.Comment: 7 pages, 3 figures, to be published in Euro.Phys.Let

A review of wetting versus adsorption, complexions, and related phenomena: the rosetta stone of wetting

This paper reviews the fundamental concepts and the terminology of wetting. In particular, it focuses on high temperature wetting phenomena of primary interest to materials scientists. We have chosen to split this review into two sections: one related to macroscopic (continuum) definitions and the other to a microscopic (or atomistic) approach, where the role of chemistry and structure of interfaces and free surfaces on wetting phenomena are addressed. A great deal of attention has been placed on thermodynamics. This allows clarification of many important features, including the state of equilibrium between phases, the kinetics of equilibration, triple lines, hysteresis, adsorption (segregation) and the concept of complexions, intergranular films, prewetting, bulk phase transitions versus “interface transitions”, liquid versus solid wetting, and wetting versus dewetting.Seventh Framework Programme (European Commission) (Grant FP7-NMP-2009-CSA-23348-MACAN

Browsing the world wide web in a non-visual environment

Presented at the 4th International Conference on Auditory Display (ICAD), Palo Alto, California, November 2-5, 1997.We have been investigating building a non-visual browsing environment for the WWW, specifically one that relies heavily on audio for information delivery and feedback. The idea is that with an unobtrusive browser, a user may listen to the WWW in the background, just as many people now listen to the radio while doing other tasks. This paper discusses two of the major issues which are faced in such a system, how to render HTML documents using audio, and how to provide a non-visual browsing interface for the WWW. We have implemented a prototype system as part of the Web-based Interactive Radio Environment, which includes our approaches to these issues

How users assess web pages for information-seeking

In this paper, we investigate the criteria used by online searchers when assessing the relevance of web pages for information-seeking tasks. Twenty four participants were given three tasks each, and indicated the features of web pages which they employed when deciding about the usefulness of the pages in relation to the tasks. These tasks were presented within the context of a simulated work-task situation. We investigated the relative utility of features identified by participants (web page content,structure and quality), and how the importance of these features is affected by the type of information-seeking task performed and the stage of the search. The results of this study provide a set of criteria used by searchers to decide about the utility of web pages for different types of tasks. Such criteria can have implications for the design of systems that use or recommend web pages

Influence of step structure on preferred orientation relationships of Ag deposited on Ni(111)

Previous studies have shown that the orientation relationships which develop in hetero-epitaxy are strongly influenced by the alignment of steps in the deposit with the pre-existing steps of the substrate. In this paper we use a combination of experiments with computer simulations to identify the important influence of substrate step structure on the eventual orientation relationships that develop in the deposit. We have made use of Ag deposited on Ni as it has been used extensively as a model system for the study of hetero-epitaxy. This system displays a large lattice mismatch of 16%. It is shown that on any surface vicinal to Ni(111), which has two possible kinds of steps (A-steps with {100} ledges and B-steps with {111} ledges), a Ag deposit adopts a single orientation relationship because only A-steps remain stable in the presence of Ag.Comment: Acta Materialia, Elsevier, In pres

What environmental transmission electron microscopy measures and how this links to diffusivity: thermodynamics versus kinetics

Environmental or in situ electron microscopy means the observation of material in its native environment, which can be gaseous or liquid, as compared to more traditional post-mortem electron microscopy carried out under (ultra) high vacuum conditions. Experiments can be performed on bulk samples in scanning electron microscopes or on thinned samples in transmission (scanning) electron microscopes. In the latter, the movement, in real time and in situ, of nanoparticles, clusters or even single atoms on the surfaces of thinned material or within a liquid can be observed. It is argued here that due to the changes that a specimen typically undergoes during in situ observation, electron irradiation effects are difficult to evaluate and so thermodynamic parameters, such as activation energies for diffusion and segregation, which are governed by movements of only a minority of atoms in the specimen, cannot be reliably determined because of the potentially high energy transfer by the irradiating electron beam to some atoms in the sample. In order to measure diffusivities reliably, radiation effects and surface diffusion need to be excluded or kept minimal so as not to disturb the measurements, which can be checked by repeating experiments and comparing results as function of time and dose for the same position, at different positions or for different specimen thicknesses. Kinetic measurements of nucleation and growth phenomena, such as Ostwald ripening, are possibly influenced to a far lesser degree by irradiation effects, as a majority of atoms actively participate in these processes and if a small fraction of them will get extra energy from the irradiation process then their influence on the overall kinetics may be rather minor

Динамическая устойчивость работы ветроэлектростанций в составе электроэнергетических систем

Объектом исследования являются: модели энергосистем, тепловая электростанция мощностью 556 МВт. Цель работы – исследование динамической устойчивости крупных ветроферм, работающих в энергосистеме, оценка влияния внедрения ветроэлектростанций на динамическую устойчивость синхронных генераторов энергосистемы. Выпускная квалификационная работа выполнена с помощью программ MS Excel, MS Visio, PSS/E, EnergyPRO Software в текстовом редакторе MS Word.Objects of the research: power system models, thermal power station with total capacity 556 MW. Object of the work – investigation of dynamic stability of large wind farms, working in power system, evaluation of wind farms implementation influence on large synchronous generators of power system. Master thesis work was performed in MS Word, MS Excel, MS Visio, PSS/E, EnergyPRO Software

Normal scaling in globally conserved interface-controlled coarsening of fractal clusters

Globally conserved interface-controlled coarsening of fractal clusters exhibits dynamic scale invariance and normal scaling. This is demonstrated by a numerical solution of the Ginzburg-Landau equation with a global conservation law. The sharp-interface limit of this equation is volume preserving motion by mean curvature. The scaled form of the correlation function has a power-law tail accommodating the fractal initial condition. The coarsening length exhibits normal scaling with time. Finally, shrinking of the fractal clusters with time is observed. The difference between global and local conservation is discussed.Comment: 4 pages, 3 eps figure

Calculation and validation of a grain boundary complexion diagram for Bi-doped Ni

A grain boundary (GB) “phase” (complexion) diagram is computed via a lattice type statistical thermodynamic model for the average general GBs in Bi-doped Ni. The predictions are calibrated with previously-reported density functional theory calculations and further validated by experiments, including both new and old aberration-corrected scanning transmission electron microscopy characterization results as well as prior Auger electron spectroscopy measurements. This work supports a major scientific goal of developing GB complexion diagrams as an extension to bulk phase diagrams and a useful materials science tool