A formal approach to AADL model-based software engineering

International Journal on Software Tools for Technology Transfer - Formal methods have become a recommended practice in safety-critical software engineering. To be formally verified, a system should...     

Concentration fields in the solidification processing of metal matrix composites

A numerical investigation of the solidification of a binary alloy (Al-1.0 wt.% Cu) around cylindrical fibers with different fiber layouts and thermophysical properties was undertaken to gain insight into the processing of fiber-reinforced metal matrix composites. The focus of this study was on solute transport and redistribution during the solidification process, and the resulting concentration fields in the solidified alloy matrix. Change of phase in the alloy was formulated using a modified version of the temperature-transforming method for the energy equation. A source term that accounts for the solute rejection at the interface was incorporated into the solute concentration equation to model solute redistribution at the interface. Detailed results were obtained from the numerical simulations of low-(alumina) and high-(copper) conductivity fibers in inline and staggered configurations. Effects of the fiber pitch (longitudinal spacing) and transverse spacing were investigated. Higher concentrations of solute were seen to accumulate around copper fibers than for alumina fibers. With an initial, uniform concentration of 1.0 wt.% Cu in the melt, the maximum-recorded solute concentration in the domain for alumina fibers was 1.26% while that for copper fibers was 3.11%. For inline fibers, increasing the fiber pitch beyond a critical value did not change the overall shape of the local solute distribution around the fibers: the critical pitch for alumina fibers was found to be roughly 2.5 fiber diameters while that for copper was 2 fiber diameters.     

A.c. conductivity and dielectric study of LiNiPO4 synthesized by solid-state method

LiNiPO₄ compound was prepared by the conventional solid-state reaction. The sample was characterized by X-ray powder diffraction, infrared, Raman analysis spectroscopy and electrical impedance spectroscopy. The compound crystallizes in the orthorhombic system, space group Pnma with a = 10·0252(7) Å, b = 5·8569(5) Å and c = 4·6758(4) Å. Vibrational analysis was used to identify the presence of \( \mathrm{PO}_4^{3- } \) – group in this compound. The complex impedance has been measured in the temperature and frequency ranges 654–716 K and 242 Hz–5 MHz, respectively. The Z′ and Z″ vs frequency plots are well-fitted to an equivalent circuit consisting of series of combination of grains and grain boundary elements. Dielectric data were analysed using complex electrical modulus M* for the sample at various temperatures. The modulus plots are characterized by the presence of two peaks thermally activated. The frequency dependence of the conductivity is interpreted in terms of equation: \( {\sigma_{\mathrm{a}.\mathrm{c}.}}\left( \omega \right)=\left[ {{{{{\sigma_{\mathrm{g}}}}} \left/ {{\left( {1+{\tau^2}{\omega^2}} \right)}} \right.}+\left( {{{{{\sigma_{\infty }}{\tau^2}{\omega^2}}} \left/ {{1+{\tau^2}{\omega^2}}} \right.}} \right)+A{\omega^{\mathrm{n}}}} \right] \) . The near values of activation energies obtained from the analysis of M″, conductivity data and equivalent circuit confirms that the transport is through ion hopping mechanism dominated by the motion of Li⁺ in the structure of the investigated material.     

Fabrication and characterization of a planar interleaved micro-transformer with magnetic core

This paper presents the design, the fabrication and the characterization of a planar interleaved micro-transformer with an Yttrium Iron Garnet (YIG) core. The design of this micro-transformer and the manufacturing steps are presented. HFSS software is used for the conception and the simulation of the interleaved magnetic micro-transformer. It is composed of two identical windings. A bottom magnetic core is used to improve the integrated transformer performances. To form the windings, we have used a surface micromachining process. We have also used a negative photoresist (SU-8) as an insulating layer and as support for the fabrication of a bridge to connect the central end of the coils to the ground shield. The micro-transformer have been characterized with impedance meter up to 100 MHz, and completed to 1 GHz using vector network analyzer.     

Network-Level QoS Assurances Through Adaptive Allocation of CDMA Resources

In a Code Division Multiple Access (CDMA) network, multiple Mobile Hosts (MHs) can simultaneously transmit over the wireless channel by using different codes. To assure an acceptable Quality of Service (QoS) for all MHs' flows, the network usually tunes the transmit powers of all MHs to achieve a certain level of signal strength as compared to the noise and the interference (SINR) for each MH. The traditional assumption in power control schemes is that the SINR requirement is statically determined for each MH's flow. In contrast, in this paper, we propose a scheme that dynamically adapts the SINR requirements of MH's flow based on its QoS requirements and the conditions of the wireless channel between the MHs and the base station. As a result of this adaptation, we show that network-level QoS measures such as fraction of packets meeting their delay requirements and energy consumed per packet transmission are significantly better than in a scheme that statically fixes the SINR requirements. We show that the adaptation approach works well for the Matched Filter (MF) and the Minimum Mean Squared Error (MMSE) receivers. Our scheme uses a simple table-driven approach for optimally selecting the target SINR requirement for each MH at run time. The entries in the table are computed off-line using a dynamic programming algorithm with the objective of maximizing a profit function that balances the need for meeting the network-level QoS requirements and the cost of using a particular target SINR for a given transmission. Moncef Elaoud (M'97) received his B.Sc. (1988) his M.Sc. (1990) and his Ph.D. (2000) in electrical an computer engineering from the University of Wisconsin-Madison. He is currently a senior research Scientist at Telcordia Technologies' Applied Research organization. His main research interests are in the areas of quality of service, self-forming and self healing networks, auto-configuration, and mobility management in wireless and ad-hoc networks. Bechir Hamdaoui received the B.S. degrees in both electrical and mechanical engineering, and the M.S. degree in mechanical engineering from the National School of Engineering in Tunis (BAC+6+DEA, ENIT), Tunisia, in 1997 and 1998, respectively. He also received the M.S. degree in electrical and computer engineering from the University of Wiconsin, Madison, WI, in 2002, where he is currently working toward the Ph.D. degree. From 1998 to 1999, he worked as a quality control and planning engineer on power generation plant project under the supervision of FIAT Avio. His research focuses on various aspects in the area of computer networking including mobile networks, wireless communication systems, and ad hoc networks. Parameswaran Ramanathan received the B. Tech degree from the Indian Institute of Technology, Bombay, India, in 1984, and the M. S. E. and Ph. D. degrees from the University of Michigan, Ann Arbor, in 1986 and 1989, respectively. Since 1989, Dr. Ramanathan has been faculty member in the Department of Electrical & Computer Engineering, University of Wisconsin, Madison, where is presently a Full Professor. He leads research projects in the areas of sensor networks and next generation cellular technology. In 1997–98, he took a sabbatical leave to visit research groups at AT&T Laboratories and Telcordia Technologies. Dr. Ramanathan's research interests include wireless and wireline networking, real-time systems, fault-tolerant computing, and distributed systems. He is presently an Associate Editor for IEEE Transactions on Mobile Computing and Elsevier AdHoc Networks Journal. He served as an Associate Editor for IEEE Transactions on Parallel and Distributed Computing from 1996–1999. He has also served on program committees of conferences such as Mobicom, Mobihoc, International Conferences on Distributed Systems and Networks, Distributed Computing Systems, Fault-tolerant Computing Symposium, Real-time Systems Symposium, Conference on Local Computer Networks, and International Conference on Engineering Complex Computer Systems. He was the Finance and Registration Chair for the 1999 Fault-tolerant Computing Symposium. He was the program chairman of the Workshop on Architectures for Real-time Applications, 1994 and the program vice-chair for the International Workshop on Parallel and Distributed Real-time Systems, 1996. He is a member of Association of Computing Machinery and a senior member of IEEE.     

Diffusion as a method for producing architectured materials

We describe the use of controlled diffusion treatments to arrange the distribution of alloying elements within a material. The Fe–C system is particularly interesting because of the strong effect of carbon on the mechanical properties and phase stability of steel. We demonstrate, through multi-step treatments, both one-dimensional and two-dimensional distributions of carbon within steel. A sample two-dimensional architecture is prepared and characterized to demonstrate feasibility. We briefly introduce a global optimization algorithm as a method for computationally optimizing treatment schedules.     

Extreme Value Theory and Value at Risk: Application to oil market

Recent increases in energy prices, especially oil prices, have become a principal concern for consumers, corporations, and governments. Most analysts believe that oil price fluctuations have considerable consequences on economic activity. Oil markets have become relatively free, resulting in a high degree of oil-price volatility and generating radical changes to world energy and oil industries. Consequently, oil markets are naturally vulnerable to significant high price shifts. An example of such a case is the oil embargo crisis of 1973. In this newly created climate, protection against market risk has become a necessity. Value at Risk (VaR) measures risk exposure at a given probability level and is very important for risk management. Appealing aspects of Extreme Value Theory (EVT) have made convincing arguments for its use in managing energy price risks. In this paper, we model VaR for long and short trading positions in oil market by applying both unconditional and conditional EVT models to forecast Value at Risk. These models are compared to the performances of other well-known modelling techniques, such as GARCH, Historical Simulation and Filtered Historical Simulation. Both conditional EVT and Filtered Historical Simulation procedures offer a major improvement over the conventional methods. Furthermore, GARCH(1, 1)-t model may provide equally good results which are comparable to two combined procedures. Finally, our results confirm the importance of filtering process for the success of standard approaches.     

WCDS‐DCR: an energy‐efficient data‐centric routing scheme for wireless sensor networks

Wireless sensor networks (WSNs) typically consist of a large number of battery‐constrained sensors often deployed in harsh environments with little to no human control, thereby necessitating scalable and energy‐efficient techniques. This paper proposes a scalable and energy‐efficient routing scheme, called WCDS‐DCR, suitable for these WSNs. WCDS‐DCR is a fully distributed, data‐centric, routing technique that makes use of an underlying clustering structure induced by the construction of WCDS (Weakly Connected Dominating Set) to prolong network lifetime. It aims at extending network lifetime through the use of data aggregation (based on the elimination of redundant data packets) by some particular nodes. It also utilizes both the energy availability information and the distances (in number of hops) from sensors to the sink in order to make hop‐by‐hop, energy‐aware, routing decisions. Simulation results show that our solution is scalable, and outperforms existing schemes in terms of network lifetime. Copyright © 2010 John Wiley & Sons, Ltd.     

Fabrication and properties of integrated magnetic inductors using an RLC model which takes into account eddy current

This article concerns the development, the fabrication and the characterization of integrated inductors using magnetic layers for use in power electronics. Properties of inductors were extracted using an electrical model which takes into account eddy current. Inductors with one and two magnetic layers were fabricated with thicknesses varying between 100 and 500 µm. Measurements carried out with a Vector Network Analyzer up to 350 MHz are presented. The results show that the use of one magnetic layer allows the inductance of the coreless inductor to be multiplied by two and an inductor with two magnetic layers allows the inductance of the coreless inductor to be multiplied by 15 for 500 µm magnetic thickness layers.