A Closed‐Form Solution to Single Scattering for General Phase Functions and Light Distributions

Due to the intricate nature of the equation governing light transport in participating media, accurately and efficiently simulating radiative energy transfer remains very challenging in spite of its broad range of applications. As an alternative to traditional numerical estimation methods such as ray‐marching and volume‐slicing, a few analytical approaches to solving single scattering have been proposed but current techniques are limited to the assumption of isotropy, rely on simplifying approximations and/or require substantial numerical precomputation and storage. In this paper, we present the very first closed‐form solution to the air‐light integral in homogeneous media for general 1‐D anisotropic phase functions and punctual light sources. By addressing an open problem in the overall light transport literature, this novel theoretical result enables the analytical computation of exact solutions to complex scattering phenomena while achieving semi‐interactive performance on graphics hardware for several common scattering modes.     

Innovative directions in self-organized distributed multimedia systems

The way by which multimedia contents are produced, delivered across networks, and consumed by intended users have shifted significantly during the past 10 years. In this paper we postulate that, in the near future, flexible and self-organizing facilities will play a dominating role in distributed multimedia systems. We discuss how such systems can be designed, using a three-layer (sensor, distribution, and user layer) architecture, SOMA (Self Organizing Multimedia Architecture), as an example. We also present innovative directions in three main aspects of self-organized multimedia systems: (i) the self-organizing aspects of multimedia user communities, e.g., the wisdom, intentions, and needs of users; (ii) a fresh look at video streams that treat them as a collection of units that can be composed taking user and network aspects into account; and (iii) new delivery paradigms and how self-organization and multimedia delivery can be combined.     

Optimization strategies for discrete multi-material stiffness optimization

Design of composite laminated lay-ups are formulated as discrete multi-material selection problems. The design problem can be modeled as a non-convex mixed-integer optimization problem. Such problems are in general only solvable to global optimality for small to moderate sized problems. To attack larger problem instances we formulate convex and non-convex continuous relaxations which can be solved using gradient based optimization algorithms. The convex relaxation yields a lower bound on the attainable performance. The optimal solution to the convex relaxation is used as a starting guess in a continuation approach where the convex relaxation is changed to a non-convex relaxation by introduction of a quadratic penalty constraint whereby intermediate-valued designs are prevented. The minimum compliance, mass constrained multiple load case problem is formulated and solved for a number of examples which numerically confirm the sought properties of the new scheme in terms of convergence to a discrete solution.     

To bee or not to bee—comments on “Discrete optimum design of truss structures using artificial bee colony algorithm”

An Artificial Bee Colony algorithm was presented by Sonmez (Struct Multidisc Optim 43:85–97, 2011) for solving discrete truss design problems. It was numerically tested on four benchmark examples and concluded to be robust and efficient. We compare the Artificial Bee Colony algorithm numerically to three alternative heuristics on the same benchmark examples. The most advanced heuristics presented herein find equally good, or better, designs compared to those presented in Sonmez (Struct Multidisc Optim 43:85–97, 2011). However, for the largest benchmark example, we use four orders of magnitude fewer function evaluations.     

Model selection for the LS-SVM. Application to handwriting recognition

The support vector machine (SVM) is a powerful classifier which has been used successfully in many pattern recognition problems. It has also been shown to perform well in the handwriting recognition field. The least squares SVM (LS-SVM), like the SVM, is based on the margin-maximization principle performing structural risk minimization. However, it is easier to train than the SVM, as it requires only the solution to a convex linear problem, and not a quadratic problem as in the SVM. In this paper, we propose to conduct model selection for the LS-SVM using an empirical error criterion. Experiments on handwritten character recognition show the usefulness of this classifier and demonstrate that model selection improves the generalization performance of the LS-SVM.     

Soft Textured Shadow Volume

Efficiently computing robust soft shadows is a challenging and time consuming task. On the one hand, the quality of image-based shadows is inherently limited by the discrete property of their framework. On the other hand, object-based algorithms do not exhibit such discretization issues but they can only efficiently deal with triangles having a constant transmittance factor. This paper addresses this limitation. We propose a general algorithm for the computation of robust and accurate soft shadows for triangles with a spatially varying transmittance. We then show how this technique can be efficiently included into object-based soft shadow algorithms. This results in unified object-based frameworks for computing robust direct shadows for both standard and perforated triangles in fully animated scenes.     

Interacting services: From specification to execution

Interacting services play a key role to realize business process integration among different business partners by means of electronic message exchange. In order to provide seamless integration of these services, the messages exchanged as well as their dependencies must be well-defined. Service choreographies are a means to describe the allowed conversations. This article presents a requirements framework for service choreography languages, along which existing choreography languages are assessed. The requirements framework provides the basis for introducing the language BPEL4Chor, which extends the industry standard WS-BPEL with choreography-specific concepts. A validation is provided and integration with executable service orchestrations is discussed.     

Die unbekannte dritte Dimension: Geländehöhen,Gewässertiefen und Dynamik österreichischer Donaulandschaften vor der Regulierung

River landscapes are multidimensional ecosystems characterized by diverse spatio-temporal interrelations. Longitudinal interactions along the river continuum and lateral exchange processes between river and floodplain are common focal points in river restoration projects. Vertical interactions, such as between aquatic habitats and river bottom (hyporheic interstitial) or between groundwater and terrestrial habitats, are often only addressed in planning schemes, if the impairments of ecological functions and human uses are already evident. This partly reflects the dearth of well-founded basic data on the configuration of river landscapes prior to regulation in the vertical dimension. Consequently, only few reference data are available for designing adapted restoration measures.     

Adjoint-based fluid flow control and optimisation with lattice Boltzmann methods

A lattice Boltzmann (LB) framework to solve fluid flow control and optimisation problems numerically is presented. Problems are formulated on a mesoscopic basis. In a side condition, the dynamics of a Newtonian fluid is described by a family of simplified Boltzmann-like equations, namely BGK–Boltzmann equations, which are linked to an incompressible Navier–Stokes equation. It is proposed to solve the non-linear optimisation problem by a line search algorithm. The needed derivatives are obtained by deriving the adjoint equations, referred to as adjoint BGK–Boltzmann equations. The primal equations are discretised by standard lattice Boltzmann methods (LBM) while for the adjoint equations a novel discretisation strategy is introduced. The approach follows the main ideas behind LBM and is therefore referred to as adjoint lattice Boltzmann methods (ALBM). The corresponding algorithm retains most of the basic features of LB algorithms. In particular, it enables a highly-efficient parallel implementation and thus solving large-scale fluid flow control and optimisation problems. The overall solution strategy, the derivation of a prototype adjoint BGK–Boltzmann equation, the novel ALBM and its parallel realisation as well as its validation are discussed in detail in this article. Numerical and performance results are presented for a series of steady-state distributed control problems with up to approximately 1.6 million unknown control parameters obtained on a high performance computer with up to 256 processing units.     

A time-efficient method for combinedt 1 andt 2 measurement in magnetic resonance imaging: Evaluation for multiparameter tissue characterization

A new magnetic resonance imaging high-resolution sequence is presented that allows for the collection of all data for determination ofT ₁ and as well as for multiexponentialT ₂ analysis within one measurement cycle.Noise preprocessing is performed in order to avoid systematic errors in relaxation parameter analysis and to increase the interexperimental reproducibility of the results. ForT ₂ analysis, an optimized Marquardt algorithm is used, in combination with image processing methods for both automatic detection of voxels with partial volume effects, and for speedup of the iterative nonlinear regression steps. Determination of longitudinal relaxation time is based on a sophisticated signal intensity ratio technique that computesT ₁ as the mean of up to eight individualT ₁ values, each weighted with its relativeT ₂ decay. Relative proton density is computed using results of the evaluations of both relaxation times. Validation of the method is accomplished by comparing phantom measurements with reference data acquired with spectroscopic sequences.In vivo examples of the computed parameter images taken from a study of experimental cerebral infarcts in rats are presented.The method allows one to acquire high-resolution parameter images within a measurement time that is tolerable even in clinical routine. Furthermore, the chosen evaluation concepts guarantee a short computation time. Therefore, an on-line computation of the parameter images and, in consequence, their direct use for diagnostic purposes appears feasible.