Petri net based verification of distributed algorithms: An example

A technique to model and to verify distributed algorithms is suggested. This technique (based on Petri nets) reduces the modelling and analysis effort to a reasonable level. The paper outlines the technique using the example of a typical network algorithm, theecho algorithm.Supported by the DFG-projects Verteilte Algorithmen and Konsensalgorithmen     

Exception handling in workflow management systems

Fault tolerance is a key requirement in process support systems (PSS), a class of distributed computing middleware encompassing applications such as workflow management systems and process centered software engineering environments. A PSS controls the flow of work between programs and users in networked environments based on a “metaprogram” (the process). The resulting applications are characterized by a high degree of distribution and a high degree of heterogeneity (properties that make fault tolerance both highly desirable and difficult to achieve). We present a solution for implementing more reliable processes by using exception handling, as it is used in programming languages, and atomicity, as it is known from the transaction concept in database management systems. We describe the mechanism incorporating both transactions and exceptions and present a validation technique allowing to assess the correctness of process specifications     

IRIS: illustrative rendering for integral surfaces

Integral surfaces are ideal tools to illustrate vector fields and fluid flow structures. However, these surfaces can be visually complex and exhibit difficult geometric properties, owing to strong stretching, shearing and folding of the flow from which they are derived. Many techniques for non-photorealistic rendering have been presented previously. It is, however, unclear how these techniques can be applied to integral surfaces. In this paper, we examine how transparency and texturing techniques can be used with integral surfaces to convey both shape and directional information. We present a rendering pipeline that combines these techniques aimed at faithfully and accurately representing integral surfaces while improving visualization insight. The presented pipeline is implemented directly on the GPU, providing real-time interaction for all rendering modes, and does not require expensive preprocessing of integral surfaces after computation.     

Time‐multiplexed tiled projection system with improved pixel and spatial resolution

We propose two methods to increase the pixel and spatial resolution of Digital Micromirror Devices (DMD)‐based projectors by utilizing the large bandwidth provided by their high pattern rates. By varying the intensity of the illumination for each binary pattern displayed on the DMD, the time required to display an 8‐bit grayscale image can be reduced by up to factor 32 compared to using constant illumination and binary pulse‐width modulation (BPWM). The high image rate projection is then spatially separated by either using a galvanometer scanner or sequentially illuminating the DMD from different directions, thus creating multiple independently addressable projections which are then tiled to form a larger, higher resolution image.     

Evaluating the relationship between chemical exposure and cryptorchidism

One method for the evaluation of complex environmental and health datasets is the discrete mathematical method Hasse diagram technique based on partial orders. The introduced software program package is named PyHasse. In this paper we evaluate a possible human association between maternal exposure to organochlorine compounds used as pesticides and cryptorchidism among male children in Finland and Denmark. We identified differences in comparable and incomparable objects and quantified these differences by the software tool Similarity Analysis in the program PyHasse. Furthermore we interpreted the corresponding Hasse diagrams concerning chosen “striking objects”. We found the position of the chemicals AHCH (alpha-Hexachlorohexane), CHCE (cis-Heptachloroepoxide), DIEL (Dieldrin), and MIRE (Mirex) has some influence on the differentiation of the Hasse diagrams and hence of each two datasets analyzed. The largest disparities can be observed when we compare the Finnish and Danish datasets concerning cryptorchidism. The disparities are demonstrated in the corresponding Hasse diagrams.     

ConceptGraph: A Formal Model for Interpretation and Reasoning During Visual Analysis

In order to discuss the kinds of reasoning a visualization supports and the conclusions that can be drawn within the analysis context, a theoretical framework is needed that enables a formal treatment of the reasoning process. Such a model needs to encompass three stages of the visualization pipeline: encoding, decoding and interpretation. The encoding details how data are transformed into a visualization and what can be seen in the visualization. The decoding explains how humans construct graphical contexts inside the depicted visualization and how they interpret them assigning meaning to displayed structures according to a formal reasoning strategy. In the presented model, we adapt and combine theories for the different steps into a unified formal framework such that the analysis process is modelled as an assignment of meaning to displayed structures according to a formal reasoning strategy. Additionally, we propose the ConceptGraph, a combined graph-based representation of the finite-state transducers resulting from the three stages, that can be used to formalize and understand the reasoning process. We apply the new model to several visualization types and investigate reasoning strategies for various tasks.     

On mesh-free valley surface extraction with application to low frequency sound simulation

Crease surfaces describe extremal structures of 3D scalar fields. We present a new region-growing-based approach to the meshless extraction of adaptive nonmanifold valley and ridge surfaces that overcomes limitations of previous approaches by decoupling point seeding and triangulation of the surface. Our method is capable of extracting valley surface skeletons as connected minimum structures. As our algorithm is inherently mesh-free and curvature adaptive, it is suitable for surface construction in fields with an arbitrary neighborhood structure. As an application for insightful visualization with valley surfaces, we choose a low frequency acoustics simulation. We use our valley surface construction approach to visualize the resulting complex-valued scalar pressure field for arbitrary frequencies to identify regions of sound cancellation. This provides an expressive visualization of the topology of wave node and antinode structures in simulated acoustics.     

Listener-based analysis of surface importance for acoustic metrics

Acoustic quality in room acoustics is measured by well defined quantities, like definition, which can be derived from simulated impulse response filters or measured values. These take into account the intensity and phase shift of multiple reflections due to a wave front emanating from a sound source. Definition (D50) and clarity (C50) for example correspond to the fraction of the energy received in total to the energy received in the first 50 ms at a certain listener position. Unfortunately, the impulse response measured at a single point does not provide any information about the direction of reflections, and about the reflection surfaces which contribute to this measure. For the visualization of room acoustics, however, this information is very useful since it allows to discover regions with high contribution and provides insight into the influence of all reflecting surfaces to the quality measure. We use the phonon tracing method to calculate the contribution of the reflection surfaces to the impulse response for different listener positions. This data is used to compute importance values for the geometry taking a certain acoustic metric into account. To get a visual insight into the directional aspect, we map the importance to the reflecting surfaces of the geometry. This visualization indicates which parts of the surfaces need to be changed to enhance the chosen acoustic quality measure.We apply our method to the acoustic improvement of a lecture hall by means of enhancing the overall speech comprehensibility (clarity) and evaluate the results using glyphs to visualize the clarity (C50) values at listener positions throughout the room.