Dmitry Medvedev

Influence of external flows on crystal growth: numerical investigation.

We use a combined phase-field-lattice-Boltzmann scheme [Medvedev and Kassner, Phys. Rev. E 72, 056703 (2005)] to simulate nonfaceted crystal growth from an undercooled melt in external flows. Selected growth parameters are determined numerically. For growth patterns at moderate to high undercooling and relatively large anisotropy, the values of the tip radius and selection parameter plotted as a function of the Péclet number fall approximately on single curves. Hence, it may be argued that a parallel flow changes the selected tip radius and growth velocity solely by modifying (increasing) the Péclet number. This has interesting implications for the availability of current selection theories as predictors of growth characteristics under flow. At smaller anisotropy, a modification of the morphology diagram in the plane of undercooling versus anisotropy is observed. The transition line from dendrites to doublons is shifted in favor of dendritic patterns, which become faster than doublons as the flow speed is increased, thus rendering the basin of attraction of dendritic structures larger. For small anisotropy and Prandtl number, we find oscillations of the tip velocity in the presence of flow. On increasing the fluid viscosity or decreasing the flow velocity, we observe a reduction in the amplitude of these oscillations.

Space Physics Interactive Data Resource—SPIDR

SPIDR (Space Physics Interactive Data Resource) is a standard data source for solar-terrestrial physics, functioning within the framework of the ICSU World Data Centers. It is a distributed database and application server network, built to select, visualize and model historical space weather data distributed across the Internet. SPIDR can work as a fully-functional web-application (portal) or as a grid of web-services, providing functions for other applications to access its data holdings.

Exploiting satellite altimetry in coastal ocean through the ALTICORE project

Altimeter-derived information on sea level and sea state could be extremely important for resolving the complex dynamics of the coastal ocean. Satellite altimetry was not originally conceived with coastal ocean in mind, but future missions (AltiKa and CryoSat-2) promise much improved nearshore capabilities. A current priority is to analyze the existing, under-exploited, 15-year global archive of coastal altimeter data to draw recommendations for these missions. There are intrinsic difficulties in processing and interpretation of the data, e.g.: the proximity of land, control by the seabed, and rapid variations due to tides and atmospheric effects. But there are also unexploited possibilities, including higher along track data rates and multi-altimetry scenarios that need to be explored. There are also difficulties of accessing and manipulating data from multiple sources, many of which undergo regular revision and enhancement. In response to these needs, the ALTICORE (ALTImetry for COastal REgions - www.alticore.eu) project started in December 2006, funded for two-years by the European INTAS scheme (www.intas.be). The overall aim of ALTICORE is to build up capacity for provision of altimeter-based information in support of coastal ocean studies in some European Seas (Mediterranean, Black, Caspian, White and Barents). ALTICORE will also contribute to improved cooperation between Europe and Eastern countries and enhance networking of capacity in the area of satellite altimetry. This paper discusses the approach, summarizes the planned work and shows how the coastal community should eventually benefit from better access to improved altimeter-derived information.

Electrochemical Approach for Analyzing Electrolyte Transport Properties and Their Effect on Protonic Ceramic Fuel Cell Performance

The design and development of highly conductive materials with wide electrolytic domain boundaries are among the most promising means of enabling solid oxide fuel cells (SOFCs) to demonstrate outstanding performance across low- and intermediate-temperature ranges. While reducing the thickness of the electrolyte is an extensively studied means for diminishing the total resistance of SOFCs, approaches involving an improvement in the transport behavior of the electrolyte membranes have been less-investigated. In the present work, a strategy for analyzing the electrolyte properties and their effect on SOFC output characteristics is proposed. To this purpose, a SOFC based on a recently developed BaCe0.5Zr0.3Dy0.2O3-δ proton-conducting ceramic material was fabricated and tested. The basis of the strategy consists of the use of traditional SOFC testing techniques combined with the current interruption method and electromotive force measurements with a modified polarization-correction assessment. This allows one to determine simultaneously such important parameters as maximal power density; ohmic and polarization resistances; average ion transport numbers; and total, ionic, and electronic film conductivities and their activation energies. The proposed experimental procedure is expected to expand both fundamental and applied basics that could be further adopted to improve the technology of electrochemical devices based on proton-conducting electrolytes.

Simulating Mobile Dendrites in a Flow

Abstract We propose a scheme for simulation of the solute-driven dendritic solidification which accounts for the flows of liquid and motion of growing dendrites. The scheme is based on the multiphase-field method for calculating the solidification and the lattice Boltzmann method to simulate the fluid flows. Motion and rotation of solid grains is possible.

Environmental scenario search and visualization

We have developed Environmental Scenario Search Engine (ESSE) for parallel data mining of a set of conditions inside distributed, very large databases from multiple environmental domains. The prime goal for ESSE design is to allow a user to query the environmental data archives in human linguistic terms. The mapping between the human language and the computer system involves fuzzy logic. Imagine for example that the end user doesnt need all of the weather data covering the Moscow region for the last 50 years, but rather needs an example of an atmospheric front near Moscow. Further imagine that this user needs satellite images of the front and he wants to know how often such fronts occur or if they have been increasing in the last 10 years. ESSE data mining and visualization portal combines metadata search, interactive fuzzy scenario query editor and event visualization system. Visualization system is implemented as MS Windows application based on NASA World Wind 3D globe and as a web application built upon OGC WMS and Microsoft Virtual Earth control.

Transparent Data Cube for Spatiotemporal Data Mining and Visualization

Data mining and visualization in very large spatiotemporal databases requires three kinds of computing parallelism: file system, data processor, and visualization or rendering farm. Transparent data cube combines on the same hardware a database cluster for active storage of spatiotemporal data with an MPI compute cluster for data processing and rendering on a tiled-display video wall. This approach results in a scalable and inexpensive architecture for interactive analysis and high-resolution mapping of environmental and remote sensing data which we use for comparative study of the climate and vegetation change.

Integrating and mining distributed environmental archives on Grids

The solar‐terrestrial physics distributed database for the ICSU World Data Centers, and the NCEP/NCAR climate re‐analysis data have been integrated into standard Grid environments using the OGSA‐DAI framework. A set of algorithms and software tools for distributed querying and mining environmental archives using the UNIDATA Common Data Model concepts has been developed. In addition, the toolkit enables querying the data using meaningful ‘human linguistic’ terms. Copyright

ALTICORE - A consortium serving european seas with coastal altimetry

In this paper, we describe the ALTICORE (value added satellite ALTImetry in COastal REgions) initiative, a consortium aiming at providing high quality coastal altimetry over some European seas. Taking the Ligurian Sea in the NW Mediterranean as an example, which acts as a test zone for this work, we show the improvement in availability and quality of ENVISAT data, through our processing, when compared with the official altimetric products delivered by AVISO. We also introduce the building concepts of solutions for data search, extraction, update and delivery based on web-services. This grid-type infrastructure is being designed within ALTICORE.

Proton-Conducting Electrolytes for Solid Oxide Fuel Cell Applications

The necessity for reducing the operating temperatures of solid oxide fuel cells (SOFCs) below 800 °C is widely proposed in the last years. To this aim, proton-conducting oxides have gained widespread interest as the electrolyte materials, acting as an alternative to oxygen ion conductors. High-temperature proton conductors, owing to their lower activation energy for proton conduction, can achieve high conductivity at relatively low temperatures compared to their oxygen ion-conducting counterparts. In this chapter, the recent advances in the field of solid oxide proton-conducting materials that belong to the class of perovskite-based materials (such as doped BaCeO3, BaZrO3, BaCeO3–BaZrO3 SrCeO3, and LaScO3) and to other classes of materials (such as doped Ba2In2O5, CeO2, and LaNbO4) are presented and analyzed.