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Wireless Internet access based on wireless LAN or Bluetooth networks will become popular within the next few years. New services will be offered using location and personal profiles to filter Internet access. Moreover, "Push" services will allow unsolicited event-based information transfer depending on user configurations. We have introduced such services as "The Mobile Fairguide" during CeBIT 2001 in a Bluetooth network that covered a full hall of 25,000 m2 with 130 base stations. We were able to show that Bluetooth is a usable technology for such applications, especially with PDAs as terminal devices. Moreover, we tested our architecture in a live scenario with respect to scalability and mobility.

We show that real-space analysis of lattice images in terms of multidimensional vectors rests on a small number of physically significant dimensions, each representing the contribution of a characteristic pattern forming a basis vector. In many cases, these basis vectors can be linked to “spatial periodicities”, and expressed in terms of conventional formalisms of dynamical scattering. This provides a link between the more abstract (but convenient) real-space image analysis and the more familiar formalisms of image formation in terms of Bloch waves. Within this framework, the simplest implementations of QUANTITEM and Chemical Mapping may be viewed as limiting cases of a more general approach. This helps delineate the application domain for each. The paper is illustrated by reference to the Al x Ga 1 − x As system in the 〈1 0 0〉, 〈1 1 0〉 and 〈1 1 1〉 projections. The historically popular 〈1 1 0〉 projection is shown to be the most complex for quantitative data extraction.

Let S be a finite subset of a lattice and let vs(L), the number of points of S ∩ L for each line L, denote the discrete Radon transform of S. The problem is to reconstruct S from a knowledge (possibly noisy) of the restriction of vs to a subset L of the set of all lines in any of a few given directions through the lattice. Reconstructing a density from its line integrals is a well-understood problem, but discreteness causes many difficulties and precludes use of continuous Radon inversion algorithms. Indeed it has been shown that when the directions are main directions of the lattice, the case for most applications, the problem is finite but is NP-hard, so that any reconstruction algorithm will surely have to consist of exponentially many steps in the size of S.We address this problem by looking instead for a fuzzy set S with the given line sums, i.e. a function f(z) with 0 ⩽ f(z) ⩽ 1 for all points z in the lattice, for which Vf(L)  vs(L). The set of all such f forms a convex set and those f = χs with each f(z) ϵ {0, 1} are extreme points. Finding a fuzzy set f with the given line sums is a linear programming problem and so there are efficient algorithms for finding f or proving that no such f (and hence no S) exists with the given line sums.If S is an additive set with respect to L, i.e. if we can write S = {z ∑LϵLϵzg(L) > 0} for some functional g on L, we show that there is only one fuzzy set f with the given line sums. We prove here that if S is not additive then there are many fuzzy sets with the given line sums, although there still may be only one actual set. Linear programming methods that are based on interior point methods always produce solutions that lie in the center of the convex set of all solutions. As a result, if S is a set with given line sums and linear programming produces a solution that consists only of {0, 1} then this solution must be the original subset S, and S must be a set of uniqueness. Thus interior point LP's give a polynomial and practical way to obtain the assertion of uniqueness when strong uniqueness obtains.This problem arises in a practical situation, although it was earlier studied in the case of coordinate directions for its intrinsic interest. In the practical situation, S represents a piece of a real crystal, and the line sums in any fixed direction can be measured (possibly with uncertainties) using a transmission electron microscope.In order to study the behavior of the linear programming reconstruction algorithm and to explore the question of whether a “typical” set S with a “typical” L will be a case of uniqueness or near-uniqueness, we conducted simulation experiments. These indicate that the method is practical and reasonably efficient, at least on the examples we considered.

The influence of Cr additions on the positive temperature dependence of the flow stress and on the antiphase boundary (APB) energies of Fe3Al was investigated. Single crystals of binary Fe28 at.% Al and ternary Fe28 at.% Al6 at.% Cr were deformed in uniaxial compression between room temperature and 1273 K. The dislocation arrangement and the dissociation of superdislocations were studied by transmission electron microscopy using the weak-beam technique. The operative slip systems are discussed on the basis of direct measurements of the APB energies. Three types of fault energies of superdislocations were analyzed as a function of temperature (up to 1003 K) and chromium concentration: the nearest-neighbor APB energy in the slip plane, the next-nearest-neighbor APB energy in the slip plane and the nearest-neighbor APB energy in the cross-slip plane. A procedure for calculating APB energies from effective pair potentials is given. The calculated results are in good agreement with the experimental data.

We describe how lattice images may be used to measure the variation of the projected potential in crystalline solids in any projection, with no knowledge of the imaging conditions. This approach is applicable to many solids with atoms residing entirely on coherent lattices, in which interfacial topography or changes in composition are of interest. We present atomic-level topographic maps of Si/SiO 2 interfaces in plan-view, and compositional maps of Si/GeSi/Si quantum wells in cross-section. We conclude with a detailed discussion of the capabilities and limitations of this approach.

A method is presented which allows the configurational energy change of long-range ordered alloys to be evaluated after the successive slip of superpartial dislocations. The long-range order is described by concentration waves, and effective pair interaction parameters determined from diffuse X-ray and neutron scattering measurements on short-range ordered alloys are used in the calculation. The method is applied to determine the antiphase boundary (APB) energies of dissociated superdislocations in different slip systems for intermetallics with L1 2 , B2 and D0 3 structures. The results mostly agree with the values of APB energies obtained from measurements of the dissociation of superdislocations using the weak-beam technique of transmission electron microscopy. On the basis of the APB energies obtained experimentally and by calculation, the temperature dependence of the critical resolved shear stress is discussed.