Adaptive finite element mesh refinement techniques inthree-dimensional micromagnetic modeling

Two different methods to adaptively refine tetrahedral finite element meshes are presented. The influence of the mesh refinement on the obtained results of micromagnetic calculations is demonstrated for the case of magnetization patterns in soft magnetic platelets. The specific addition of vertices and finite elements in inhomogeneous regions is used to resolve the magnetic structure on small length scales. A method discussed in detail is the shrinking of finite elements in regions with strong inhomogeneities     

Fast multipole method for micromagnetic simulation of periodic systems

We have developed a new method for computing the magnetostatic field of an infinite array of images of an arbitrary system of charges or multipoles. The result takes the form of a Taylor expansion of the potential of a "cored array" of distant images, as is required by the fast multipole method, the most efficient method known for calculating magnetostatic fields in very large systems. The new method is much faster and simpler to implement than the usual Ewald summation or fast Fourier transform, and does not require a regular grid inside the central cell.     

Advanced patterning techniques for nanodevice fabrication

The key elements in the fabrication of future devices are lithography and pattern transfer. The continuous advances in miniaturization and increasing integration densities are a direct result of improved lithographic resolution and overlay accuracy. Electron beam direct write and e-beam projection lithography are potential candidates for the mass production of microelectronic devices with critical dimensions below 100 nm. To realize these nanometer patterns by this technology, the performance of exposure tools and resist materials should be increased. In this paper, the method of direct write e-beam lithography is demonstrated and critical issues are discussed.     

Numerical micromagnetic calculations

Solutions of certain micromagnetic problems using digital computers have been attempted in the past decades. These problems are becoming increasingly important as magnetic devices, such as magnetic bubbles, are built which require high resolution. Some problems encountered in these types of calculations are discussed.     

Advanced preprocessing techniques for linear and quadratic programming

The paper presents an overview on the preprocessing techniques of linear programming. A new reduction technique is also introduced and the presolve is extended to mixed integer and quadratic programming problems. Numerical results are presented to demonstrate the impact of presolving in interior point and simplex implementations. The demonstrative results are given on large-scale linear, mixed integer and quadratic programming test problems.Cs. Mészáros: Supported in part by Alexander von Humboldt Foundation Correspondence to: U.H. Suhl     

Reliability analysis techniques for mechanical systems

This paper discusses the application of known system reliability analysis techniques and identifies problems encountered in the practical implementation of these methods, revealing that no single technique is sufficient or even feasible in the case of complex mechanical systems. A new functional analysis method as well as a (new) criticality quantitative approach and failure mechanism analysis are presented and used to analyse an aircraft fuel system. A rigorous and detailed FMECA is still required. Besides its main function it will supply much of the valuable information for many other techniques.     

Matrix techniques for modeling ultrasonic waves in multilayeredmedia

Research into ultrasonic NDE techniques for the inspection of multilayered structures relies strongly on the use of modeling tools which calculate dispersion curves and reflection and transmission spectra. These predictions are essential to enable the best inspection strategies to be identified and their sensitivities to be evaluated. General purpose multilayer modeling tools may be developed from a number of matrix formulations which have evolved in the latter half of this century and there is now a formidable number of publications on the subject. This paper presents a review of the main developments of the matrix techniques, and their use in response and modal models, with emphasis on ultrasonics applications     

Advanced techniques for characterization of ion beam modified materials

Understanding the mechanisms of damage formation in materials irradiated with energetic ions is essential for the field of ion-beam materials modification and engineering. Utilizing incident ions, electrons, photons, and positrons, various analysis techniques, including Rutherford backscattering spectrometry (RBS), electron RBS, Raman spectroscopy, high-resolution X-ray diffraction, small-angle X-ray scattering, and positron annihilation spectroscopy, are routinely used or gaining increasing attention in characterizing ion beam modified materials. The distinctive information, recent developments, and some perspectives in these techniques are reviewed. Applications of these techniques are discussed to demonstrate their unique ability for studying ion-solid interactions and the corresponding radiation effects in modified depths ranging from a few nm to a few tens of μm, and to provide information on electronic and atomic structure of the materials, defect configuration and concentration, as well as phase stability, amorphization and recrystallization processes. Such knowledge contributes to our fundamental understanding over a wide range of extreme conditions essential for enhancing material performance and also for design and synthesis of new materials to address a broad variety of future energy applications.     

Advanced High-temperature superconducting components for microwave systems

The application of high-temperature superconducting thin films to microwave systems is expected to lead to major volume and weight savings as well as improved performance. To take full advantage of the properties that the new materials have to offer and justify the additional cooling equipment that accompanies the introduction of superconductivity, many HTS components will have to be integrated. In this paper some of the key microwave circuits that show great promise in this respect, such as multiplexers, circulators, and very narrowband filters, will be discussed and experimental results presented.     

Advanced characterization techniques for solid state lithium battery research

Solid state batteries have attracted significant attention within the battery community over the last decade, due to the feasibility of developing a new generation of rechargeable Li batteries offering safer and long-term performance. However, many scientific and technical challenges and difficulties still need to be overcome before this new technology can be used commercially. Advanced characterization techniques provide powerful tools for studying these complex and elusive chemical/physical processes in solid-state batteries. Over the last decade, researchers have explored many sophisticated ex-situ and in-situ techniques, such as synchrotron X-ray techniques, solid-state NMR techniques, neutron scattering techniques, etc., to probe the undisclosed underlying mechanisms of solid-state batteries. In this review, we present a comprehensive overview of recent advances in these three characterization techniques in solid state battery research. Some perspectives of the future evolution of the techniques are also presented.     

Evolvable social agents for bacterial systems modeling

We present two approaches to the individual-based modeling (IbM) of bacterial ecologies and evolution using computational tools. The IbM approach is introduced, and its important complementary role to biosystems modeling is discussed. A fine-grained model of bacterial evolution is then presented that is based on networks of interactivity between computational objects representing genes and proteins. This is followed by a coarser grained agent-based model, which is designed to explore the evolvability of adaptive behavioral strategies in artificial bacteria represented by learning classifier systems. The structure and implementation of the two proposed individual-based bacterial models are discussed, and some results from simulation experiments are presented, illustrating their adaptive properties.     

Online modeling refinement for discrete event systems

Abstract

Machine identification of discrete event systems (DES) addresses the issue of identifying an unknown system based on an externally observed sample path from the unknown system. Online Modeling Refinement studies the continuing machine identification process when the observed sample path is updated incrementally. The notion of information embedded in a sample path is defined. By taking advantage of the structural similarity between successive observed sample paths, the computational requirement for the proposed online modeling refinement algorithm is kept minimal. An example is provided to show how identification results converge as the incrementally observed sequence is accumulated over time.     

Advanced control systems for single compressor chiller units

In this paper the problem of designing advanced control systems for increasing the performances of low capacity HVAC system with single scroll compressor is addressed. In particular, a simulation environment based on Matlab/Simulink that has been validated on a state-of-the-art experimental facility and used to design an adaptive controller for single scroll compressor, packaged air-cooled water chillers is presented. The capability of the controller to substantially increase the energy performance of the system, as well as to achieve excellent regulation performances in process applications is demonstrated.     

Advanced modulation formats for fiber optic communication systems

Choice of modulation format plays a critical role in the design and performance of fiber optic communication systems. We discuss the basic physics of electro-optic phase and amplitude modulation and derive model transfer functions for ideal and non-ideal Mach-Zehnder modulators. We describe the generation and characteristics of the standard nonreturn-to-zero (NRZ) modulation format, as well as advanced formats such as return-to-zero (RZ), carrier-suppressed RZ (CSRZ), duobinary, modified duobinary, differential phase-shift keyed (DPSK), and return-to-zero DPSK (RZ-DPSK). Finally, we discuss the relative merits of these formats with respect to a variety of system impairments.     

Computing solenoidal fields in micromagnetic simulations

In finite-difference micromagnetic simulations, the electric field originated from time variations of magnetic induction is evaluated by means of a discrete version of Faraday's law. The electric field can be then calculated as the convolution of a tensor and the time derivative of the magnetic induction. This paper presents an analytical expression for the tensor. The paper also reports on a quantitative test of the tensor that simulates the electric field of an oscillating magnetic point dipole.     

Discretization errors in numerical micromagnetic models

Numerical micromagnetic models attempt to determine coercive force, reversal modes, the number of stable magnetic states of particles, and the effect of particle interaction. These models can have considerable discretization error. In some cases, the calculated equilibrium states change considerably when the number of elements is increased. An analysis of three types of discretization errors suggests a measure of the accuracy of the models     

Global optimization and modeling techniques for planar multilayered dielectric structures

We present a multilevel global optimization strategy for synthesizing planar multilayered dielectric structures. A low discrepancy sequence of sample points with uniform variable space coverage allows a global-level search while systematic refinement using gradient-based techniques identifies optima at the local level. Since efficient local optimization is important for this method, a fast calculation approach based on mode matching is presented; this also facilitates the compact derivation of analytical gradients. The approach is compared with genetic and simulated annealing algorithms through an antireflection coating design. The method proves to be competitive in terms of its performance, nonadaptive algorithm, and ability to track local solutions.