19 research outputs found
Remanence Increase in SrFeO/Fe Exchange-Decoupled Hard-Soft Composite Magnets Owing to Dipolar Interactions
In the search for improved permanent magnets, fueled by the geostrategic and
environmental issues associated with rare-earth-based magnets, magnetically
hard (high anisotropy)-soft (high magnetization) composite magnets hold promise
as alternative magnets that could replace modern permanent magnets, such as
rare-earth-based and ceramic magnets, in certain applications. However, so far,
the magnetic properties reported for hard-soft composites have been
underwhelming. Here, an attempt to further understand the correlation between
magnetic and microstructural properties in strontium ferrite-based composites,
hard SrFeO (SFO) ceramics with different contents of Fe particles
as soft phase, both in powder and in dense injection molded magnets, is
presented. In addition, the influence of soft phase particle dimension, in the
nano- and micron-sized regimes, on these properties is studied. While Fe and
SFO are not exchange-coupled in our magnets, a remanence that is higher than
expected is measured. In fact, in composite injection molded anisotropic
(magnetically oriented) magnets, remanence is improved by 2.4% with respect to
a pure ferrite identical magnet. The analysis of the experimental results in
combination with micromagnetic simulations allows us to establish that the type
of interaction between hard and soft phases is of a dipolar nature, and is
responsible for the alignment of a fraction of the soft spins with the
magnetization of the hard. The mechanism unraveled in this work has
implications for the development of novel hard-soft permanent magnets
AstroGrid-D: Grid Technology for Astronomical Science
We present status and results of AstroGrid-D, a joint effort of
astrophysicists and computer scientists to employ grid technology for
scientific applications. AstroGrid-D provides access to a network of
distributed machines with a set of commands as well as software interfaces. It
allows simple use of computer and storage facilities and to schedule or monitor
compute tasks and data management. It is based on the Globus Toolkit middleware
(GT4). Chapter 1 describes the context which led to the demand for advanced
software solutions in Astrophysics, and we state the goals of the project. We
then present characteristic astrophysical applications that have been
implemented on AstroGrid-D in chapter 2. We describe simulations of different
complexity, compute-intensive calculations running on multiple sites, and
advanced applications for specific scientific purposes, such as a connection to
robotic telescopes. We can show from these examples how grid execution improves
e.g. the scientific workflow. Chapter 3 explains the software tools and
services that we adapted or newly developed. Section 3.1 is focused on the
administrative aspects of the infrastructure, to manage users and monitor
activity. Section 3.2 characterises the central components of our architecture:
The AstroGrid-D information service to collect and store metadata, a file
management system, the data management system, and a job manager for automatic
submission of compute tasks. We summarise the successfully established
infrastructure in chapter 4, concluding with our future plans to establish
AstroGrid-D as a platform of modern e-Astronomy.Comment: 14 pages, 12 figures Subjects: data analysis, image processing,
robotic telescopes, simulations, grid. Accepted for publication in New
Astronom
Matching and Evaluation of Disjunctive Predicates for Data Stream Sharing
New optimization techniques, e. g., in data stream management systems (DSMSs), make the treatment of disjunctive predicates a necessity. In this paper, we introduce and compare methods for matching and evaluating disjunctive predicates
Data Stream Sharing
Abstract. Recent research efforts in the fields of data stream processing and data stream management systems (DSMSs) show the increasing importance of processing data streams, e. g., in the e-science domain. Together with the advent of peer-to-peer (P2P) networks and grid computing, this leads to the necessity of developing new techniques for distributing and processing continuous queries over data streams in such networks. In this paper, we present a novel approach for optimizing the integration, distribution, and execution of newly registered continuous queries over data streams in grid-based P2P networks. We introduce Windowed XQuery (WXQuery), our XQuery-based subscription language for continuous queries over XML data streams supporting window-based operators. Concentrating on filtering and window-based aggregation, we present our stream sharing algorithms as well as experimental evaluation results from the astrophysics application domain to assess our approach.