The influence of a corrosive wood-cutting environment on the mechanical properties of hardmetal tools

The influence of a corrosive wood-cutting environment on the strength of hardmetals and on their behaviour under static loading conditions has been investigated. Two commercial hardmetals were tested, which differed in hard phase composition. The results show exposure to this environment to have a highly detrimental influence on the strength of both hardmetals investigated, due to localised corrosive attack which results in the formation of stress raisers. The relative loss in strength as a function of corrosion time is the same for both hardmetals. However, the performance of the two grades differ significantly when a static load is applied in this corrosive environment: the strength of the WC-Co grade remains unaffected by the applied load, while the grade containing a mixed carbide phase exhibits stress corrosion cracking which results in a further reduction in strength.     

Dislocation processes in the deformation of nanocrystalline aluminium by molecular-dynamics simulation

The mechanical behaviour of nanocrystalline materials (that is, polycrystals with a grain size of less than 100 nm) remains controversial. Although it is commonly accepted that the intrinsic deformation behaviour of these materials arises from the interplay between dislocation and grain-boundary processes, little is known about the specific deformation mechanisms. Here we use large-scale molecular-dynamics simulations to elucidate this intricate interplay during room-temperature plastic deformation of model nanocrystalline Al microstructures. We demonstrate that, in contrast to coarse-grained Al, mechanical twinning may play an important role in the deformation behaviour of nanocrystalline Al. Our results illustrate that this type of simulation has now advanced to a level where it provides a powerful new tool for elucidating and quantifying--in a degree of detail not possible experimentally--the atomic-level mechanisms controlling the complex dislocation and grain-boundary processes in heavily deformed materials with a submicrometre grain size.     

On Projection Matrices $$\mathcal{P}^k \to \mathcal{P}^2 ,k = 3,...,6, $$ and their Applications in Computer Vision

Projection matrices from projective spaces have long been used in multiple-view geometry to model the perspective projection created by the pin-hole camera. In this work we introduce higher-dimensional mappings for the representation of various applications in which the world we view is no longer rigid. We also describe the multi-view constraints from these new projection matrices (where k > 3) and methods for extracting the (non-rigid) structure and motion for each application.     

Robust vision-based localization by combining an image-retrieval system with Monte Carlo localization

In this paper, we present a vision-based approach to mobile robot localization that integrates an image-retrieval system with Monte Carlo localization. The image-retrieval process is based on features that are invariant with respect to image translations and limited scale. Since it furthermore uses local features, the system is robust against distortion and occlusions, which is especially important in populated environments. To integrate this approach with the sample-based Monte Carlo localization technique, we extract for each image in the database a set of possible viewpoints using a two-dimensional map of the environment. Our technique has been implemented and tested extensively. We present practical experiments illustrating that our approach is able to globally localize a mobile robot, to reliably keep track of the robot's position, and to recover from localization failures. We furthermore present experiments designed to analyze the reliability and robustness of our approach with respect to larger errors in the odometry.     

Prozessorientierte Wirtschaftlichkeitsuntersuchung für E-Government

E-Government economy needs to be dealt with in a multidimensional and multiperspective way. Existing evaluation concepts, though, hardly meet these pre-requisites. In this paper we give an overview of approaches and difficulties in evaluating IT-projects in public administration. Current E-Government evaluation approaches and surveys are compared as to their fitness to judge on an actual E-Government project. Based on the E-Government evaluation criteria used for the assessment of the evaluation approaches we develop a process-oriented E-Government evaluation concept which is illustrated in a mini-case.     

Performance models for network processor design

To provide a variety of new and advanced communications services, computer networks are required to perform increasingly complex packet processing. This processing typically takes place on network routers and their associated components. An increasingly central component in router design is a chip-multiprocessor (CMP) referred to as "network processor" or NP. In addition to multiple processors, NPs have multiple forms of on-chip memory, various network and off-chip memory interfaces, and other specialized logic components such as CAMs (content addressable memories). The design space for NPs (e.g., number of processors, caches, cache sizes, etc.) is large due to the diverse workload, application requirements, and system characteristics. System design constraints relate to the maximum chip area and the power consumption that are permissible while achieving defined line rates and executing required packet functions. In this paper, an analytic performance model that captures the processing performance, chip area, and power consumption for a prototypical NP is developed and used to provide quantitative insights into system design trade offs. The model, parameterized with a networking application benchmark, provides the basis for the design of a scalable, high-performance network processor and presents insights into how best to configure the numerous design elements associated with NPs.     

A proxy architecture for collaborative media streaming

Streaming media from the Internet is a successful application for end-users. With the upcoming success of mobile devices and home networking environments, cooperation among users will become more important in the future. To achieve such cooperation, explicit middleware standards have been defined. On the other hand, Internet conferencing applications do not handle collaborative streaming sessions with individual control for each user. We propose a new concept for cooperation exemplary for collaborative media streaming using IETF multimedia session control protocols together with a proxy architecture. This concept enables both synchronization among clients and flexible control to individual users.     

Fractional Fourier transforms in two dimensions

We analyze the fractionalization of the Fourier transform (FT), starting from the minimal premise that repeated application of the fractional Fourier transform (FrFT) a sufficient number of times should give back the FT. There is a qualitative increase in the richness of the solution manifold, from U(1) (the circle S1) in the one-dimensional case to U(2) (the four-parameter group of 2 x 2 unitary matrices) in the two-dimensional case [rather than simply U(1) x U(1)]. Our treatment clarifies the situation in the N-dimensional case. The parameterization of this manifold (a fiber bundle) is accomplished through two powers running over the torus T2 = S1 x S1 and two parameters running over the Fourier sphere S2. We detail the spectral representation of the FrFT: The eigenvalues are shown to depend only on the T2 coordinates; the eigenfunctions, only on the S2 coordinates. FrFT's corresponding to special points on the Fourier sphere have for eigenfunctions the Hermite-Gaussian beams and the Laguerre-Gaussian beams, while those corresponding to generic points are SU(2)-coherent states of these beams. Thus the integral transform produced by every Sp(4, R) first-order system is essentially a FrFT.