bluuebunny/crossref_metadata_2025 huggingface dataset:
Review article: The role of adipose tissue in uraemia‐related insulin resistance
Authors: MANOLESCU BOGDAN , STOIAN IRINA , ATANASIU VALERIU , BUSU CARMINA , LUPESCU OLIVERA
Published: September 2008

SUMMARY:  Adipose tissue is no longer considered to be an inert tissue of which function is to store fat. It actively secretes a number of biologic active compounds that are involved in the regulation of many processes like food intake, energy expenditure, metabolism homeostasis, immunity and blood pressure homeostasis. General metabolism alteration in patients with chronic kidney disease has a profound impact on biology of adipocytes. Chronic renal failure is a pathological condition, of which two major hallmarks are chronic inflammation and insulin resistance. In uraemic patients, adipose tissue became an important source of molecules that are responsible, at least in part, for the metabolic disturbances seen in these patients. Some of these molecules act as pro‐inflammatory agents contributing to the maintenance and enhancement of the chronic inflammatory response. These pro‐inflammatory molecules, along with other molecules secreted by the adipose tissue, have a central position in the aetiology of uraemia‐associated insulin resistance. In this review, we intend to summarize some aspects of the biology of adipokines in uraemia, with emphasis on the link between these molecules and insulin resistance.
Calcium dynamics in bovine adrenal medulla chromaffin cell secretory granules
Authors: SantoDomingo Jaime , Vay Laura , Camacho Marcial , Hernández‐SanMiguel Esther , Fonteriz Rosalba I. , Lobatón Carmen D. , Montero Mayte , Moreno Alfredo , Alvarez Javier
Published: September 2008

The secretory granules constitute one of the less well‐known compartments in terms of Ca2+ dynamics. They contain large amounts of total Ca2+, but the free intragranular [Ca2+] ([Ca2+]SG), the mechanisms for Ca2+ uptake and release from the granules and their physiological significance regarding exocytosis are still matters of debate. We used in the present work an aequorin chimera targeted to the granules to investigate [Ca2+]SG homeostasis in bovine adrenal chromaffin cells. We found that most of the intracellular aequorin chimera is present in a compartment with 50–100 μm Ca2+. Ca2+ accumulation into this compartment takes place mainly through an ATP‐dependent mechanism, namely, a thapsigargin‐sensitive Ca2+‐ATPase. In addition, fast Ca2+ release was observed in permeabilized cells after addition of inositol 1,4,5‐trisphosphate (InsP3) or caffeine, suggesting the presence of InsP3 and ryanodine receptors in the vesicular membrane. Stimulation of intact cells with the InsP3‐producing agonist histamine or with caffeine also induced Ca2+ release from the vesicles, whereas acetylcholine or high‐[K+] depolarization induced biphasic changes in vesicular [Ca2+], suggesting heterogeneous responses of different vesicle populations, some of them releasing and some taking up Ca2+ during stimulation. In conclusion, our data show that chromaffin cell secretory granules have the machinery required for rapid uptake and release of Ca2+, and this strongly supports the hypothesis that granular Ca2+ may contribute to its own secretion.
Bilateral motor resonance evoked by observation of a one‐hand movement: role of the primary motor cortex
Authors: Borroni Paola , Montagna Marcella , Cerri Gabriella , Baldissera Fausto
Published: September 2008

In humans, observation of movement performed by others evokes a subliminal motor resonant response, probably mediated by the mirror neurone system, which reproduces the motor commands needed to execute the observed movement with good spatial and temporal fidelity. Motor properties of the resonant response were here investigated with the ultimate goal of understanding the principles operating in the transformation from observation to internal reproduction of movement. Motor resonance was measured as the modulation of excitability of spinal motoneurones, evoked by the observation of a cyclic flexion‐extension of one hand. The first two experiments showed that the observation of a one‐hand movement always evoked a bimanual resonant response independent of which hand was observed and that these bilateral responses were consistently phase‐linked. H‐reflexes simultaneously recorded in right and left flexor carpi radialis muscles were always modulated ‘in‐phase’ with each other. The goal of the third experiment was to define the role of primary motor cortex in the bilateral resonant response. Bilateral H‐reflexes were recorded during a temporary inactivation induced by transcranial magnetic stimulation over the left cortical hand motor area of observers. The finding that such cortical depression abolished the H‐reflex modulation of only the right flexor carpi radialis motoneurones, leaving it unchanged on the left side, suggested that both primary motor areas were activated by the premotor cortex and transmit the resonant activation through crossed corticospinal pathways. The data provide further evidence that the subliminal activation of motor pathways induced by movement observation is organized according to general rules shared with the control of voluntary movement.
Stability of Majority Attitudes toward Multiculturalism in the Netherlands between 1999 and 2007
Authors: Breugelmans Seger M. , Van De Vijver Fons J.R. , Schalk‐Soekar Saskia G.S.
Published: September 2008

The success of multiculturalism as an ideology to deal with cultural differences depends upon the level of support for multiculturalism by majority members. It has been argued that support for multiculturalism in the Netherlands has substantially changed in response to various national and international events, such as the terrorist attacks on New York (2001), Madrid (2004), and London (2005), and the assassinations of popular politician Fortuyn (2002) and controversial movie director Van Gogh (2004). We compared survey data on Dutch majority attitudes in 1999 (n= 333), 2001 (n= 1,266), 2004 (n= 246), 2005 (n= 170), 2006 (n= 306), and 2007 (n= 464). Contrary to popular belief, we found little evidence for enduring attitude changes over the nine‐year period. Implications for studies of multiculturalism and for policy‐makers are discussed.

Le succès du multiculturalisme en tant qu’idéologie pour appréhender les différences culturelles dépend du soutien dont il bénéficie de la part de la majorité de la population. On a dit que l’approbation du multiculturalisme s’était profondément altérée aux Pays‐Bas à la suite de divers évènements nationaux et internationaux, telles que les attaques terroristes sur New York (2001), Madrid (2004) et Londres (2005), et les assassinats du politicien populaire Fortuyn (2002) et du metteur en scène controversé Van Gogh (2004). On a comparé des données d’enquête sur les attitudes majoritaires chez les Néerlandais en 1999 (n= 333), 2001 (n= 1,266), 2004 (n= 246), 2005 (n= 170), 2006 (n= 306) et 2007 (n= 464). A l’encontre de la croyance populaire, un changement d’attitudes durable est loin d’être évident sur cette période de neuf ans. On discute des conséquences pour les études sur le multiculturalisme et les projets politiques.
Impact of Relative Size and Language on the Attitudes between Nations and Linguistic Groups: The Case of Switzerland
Authors: Matser Carine , Van Oudenhoven Jan Pieter , Askevis‐Leherpeux Françoise , Florack Arnd , Hannover Bettina , Rossier Jerôme
Published: September 2008

This study explores the impact of relative size on the intra‐ and intergroup attitudes of groups who either share a language or have a different language. For that purpose, we examined international attitudes, comparing a small nation, Switzerland, and two larger nations, Germany and France. We found support for the assumption that large neighbouring nations pose a threat to the smaller nation's identity, especially when they are linguistically similar. Consequently, in line with Tajfel's Social Identity Theory (1978), the smaller nation's inhabitants evaluate those of the larger nation less positively, liking them less and perceiving them to be more arrogant than vice versa. By investigating the special case of the French‐speaking and the German‐speaking Swiss as linguistic groups within their own nation we were able to demonstrate that these groups seek support with the larger—linguistically—similar nation to defend themselves against the more direct in‐country threat to their identity. They acknowledge the similarity with the larger nation, yet keep defending their social identity by expressing a dislike for this perceived similarity.

Cette étude analyse l’impact de la taille relative de groupes partageant ou non un même langage sur les attitudes intra et inter groupes. Pour ce faire, nous avons étudié des attitudes internationales en comparant une petite nation, la Suisse, à deux grandes nations, l’Allemagne et la France. Nous avons confirmé l’hypothèse selon laquelle les grandes nations constituent une menace pour l’identité des plus petites nations voisines, particulièrement quand elles partagent une même langue. En conséquence, dans la lignée de la théorie de l’identité sociale de Tajfel (1978), les habitants de petites nations évaluent leurs homologues des plus grandes nations moins positivement, les apprécient moins et les percoivent comme étant plus arrogants que l’inverse. En enquêtant sur le cas particulier des Suisses francophones et germanophones comme groupes linguisitiques au sein de leur propre nation, nous démontrons qu’ils recherchent l’appui d’une plus grande nation similaire à eux linguistiquement pour se défendre d’une menace intérieure plus directe envers leur identité. Cependant, s’ils reconnaissent la similitude avec des plus grandes nations, ils n’en continuent pas moins à défendre leur identité sociale en exprimant une aversion pour cette similitude perçue.
Particle Level Set Advection for the Interactive Visualization of Unsteady 3D Flow
Authors: Cuntz Nicolas , Kolb Andreas , Strzodka Robert , Weiskopf Daniel
Published: September 2008

Typically, flow volumes are visualized by defining their boundary as iso‐surface of a level set function. Grid‐based level sets offer a good global representation but suffer from numerical diffusion of surface detail, whereas particle‐based methods preserve details more accurately but introduce the problem of unequal global representation. The particle level set (PLS) method combines the advantages of both approaches by interchanging the information between the grid and the particles. Our work demonstrates that the PLS technique can be adapted to volumetric dye advection via streak volumes, and to the visualization by time surfaces and path volumes. We achieve this with a modified and extended PLS, including a model for dye injection. A new algorithmic interpretation of PLS is introduced to exploit the efficiency of the GPU, leading to interactive visualization. Finally, we demonstrate the high quality and usefulness of PLS flow visualization by providing quantitative results on volume preservation and by discussing typical applications of 3D flow visualization.
Extraction Of Feature Lines On Surface Meshes Based On Discrete Morse Theory
Authors: Sahner J. , Weber B. , Prohaska S. , Lamecker H.
Published: September 2008

We present an approach for extracting extremal feature lines of scalar indicators on surface meshes, based on discrete Morse Theory. By computing initial Morse‐Smale complexes of the scalar indicators of the mesh, we obtain a candidate set of extremal feature lines of the surface. A hierarchy of Morse‐Smale complexes is computed by prioritizing feature lines according to a novel criterion and applying a cancellation procedure that allows us to select the most significant lines. Given the scalar indicators on the vertices of the mesh, the presented feature line extraction scheme is interpolation free and needs no derivative estimates. The technique is insensitive to noise and depends only on one parameter: the feature significance. We use the technique to extract surface features yielding impressive, non photorealistic images.
A Four‐level Focus+Context Approach to Interactive Visual Analysis of Temporal Features in Large Scientific Data
Authors: Muigg Philipp , Kehrer Johannes , Oeltze Steffen , Piringer Harald , Doleisch Helmut , Preim Bernhard , Hauser Helwig
Published: September 2008

In this paper we present a new approach to the interactive visual analysis of time‐dependent scientific data – both from measurements as well as from computational simulation – by visualizing a scalar function over time for each of tenthousands or even millions of sample points. In order to cope with overdrawing and cluttering, we introduce a new four‐level method of focus+context visualization. Based on a setting of coordinated, multiple views (with linking and brushing), we integrate three different kinds of focus and also the context in every single view. Per data item we use three values (from the unit interval each) to represent to which degree the data item is part of the respective focus level. We present a color compositing scheme which is capable of expressing all three values in a meaningful way, taking semantics and their relations amongst each other (in the context of our multiple linked view setup) into account. Furthermore, we present additional image‐based postprocessing methods to enhance the visualization of large sets of function graphs, including a texture‐based technique based on line integral convolution (LIC). We also propose advanced brushing techniques which are specific to the time‐dependent nature of the data (in order to brush patterns over time more efficiently). We demonstrate the usefulness of the new approach in the context of medical perfusion data.
GPU Local Triangulation: an interpolating surface reconstruction algorithm
Authors: Buchart C. , Borro D. , Amundarain A.
Published: September 2008

A GPU capable method for surface reconstruction from unorganized point clouds without additional information, called GLT (GPU Local Triangulation), is presented. The main objective of this research is the generation of a GPU interpolating reconstruction based on local Delaunay triangulations, inspired by a pre‐existing reconstruction algorithm. Current graphics hardware accelerated algorithms are approximating approaches, where the final triangulation is usually performed through either marching cubes or marching tetrahedras. GPU‐compatible methods and data structures to perform normal estimation and the local triangulation have been developed, plus a variation of the Bitonic Merge Sort algorithm to work with multi‐lists. Our method shows an average gain of one order of magnitude over previous research.
Interaction‐Dependent Semantics for Illustrative Volume Rendering
Authors: Rautek Peter , Bruckner Stefan , Gröller M. Eduard
Published: September 2008

In traditional illustration the choice of appropriate styles and rendering techniques is guided by the intention of the artist. For illustrative volume visualizations it is difficult to specify the mapping between the 3D data and the visual representation that preserves the intention of the user. The semantic layers concept establishes this mapping with a linguistic formulation of rules that directly map data features to rendering styles. With semantic layers fuzzy logic is used to evaluate the user defined illustration rules in a preprocessing step.

In this paper we introduce interaction‐dependent rules that are evaluated for each frame and are therefore computationally more expensive. Enabling interaction‐dependent rules, however, allows the use of a new class of semantics, resulting in more expressive interactive illustrations. We show that the evaluation of the fuzzy logic can be done on the graphics hardware enabling the efficient use of interaction‐dependent semantics. Further we introduce the flat rendering mode and discuss how different rendering parameters are influenced by the rule base. Our approach provides high quality illustrative volume renderings at interactive frame rates, guided by the specification of illustration rules.
Illustrative Hybrid Visualization and Exploration of Anatomical and Functional Brain Data
Authors: Jainek W. M. , Born S. , Bartz D. , Straßer W. , Fischer J.
Published: September 2008

Common practice in brain research and brain surgery involves the multi‐modal acquisition of brain anatomy and brain activation data. These highly complex three‐dimensional data have to be displayed simultaneously in order to convey spatial relationships. Unique challenges in information and interaction design have to be solved in order to keep the visualization sufficiently complete and uncluttered at the same time. The visualization method presented in this paper addresses these issues by using a hybrid combination of polygonal rendering of brain structures and direct volume rendering of activation data. Advanced rendering techniques including illustrative display styles and ambient occlusion calculations enhance the clarity of the visual output. The presented rendering pipeline produces real‐time frame rates and offers a high degree of configurability. Newly designed interaction and measurement tools are provided, which enable the user to explore the data at large, but also to inspect specific features closely. We demonstrate the system in the context of a cognitive neurosciences dataset. An initial informal evaluation shows that our visualization method is deemed useful for clinical research.
Visualizing Genome Expression and Regulatory Network Dynamics in Genomic and Metabolic Context
Authors: Westenberg M. A. , Van Hijum S. A. F. T. , Kuipers O. P. , Roerdink J. B. T. M.
Published: September 2008

DNA microarrays are used to measure the expression levels of thousands of genes simultaneously. In a time series experiment, the gene expressions are measured as a function of time. We present an application for integrated visualization of genome expression and network dynamics in both regulatory networks and metabolic pathways. Integration of these two levels of cellular processes is necessary, since it provides the link between the measurements at the transcriptional level (gene expression levels approximated from microarray data) and the phenotype (the observable characteristics of an organism) at the functional and behavioral level. The integration requires visualization approaches besides traditional clustering and statistical analysis methods. Our application can (i) visualize the data from time series experiments in the context of a regulatory network and KEGG metabolic pathways; (ii) identify and visualize active regulatory subnetworks from the gene expression data; (iii) perform a statistical test to identify and subsequently visualize pathways that are affected by differentially expressed genes. We present a case study, which demonstrates that our approach and application both facilitates and speeds up data analysis tremendously in comparison to a more traditional approach that involves many manual, laborious, and error‐prone steps.
Density Displays for Data Stream Monitoring
Authors: Hao Ming , Keim Daniel A. , Dayal Umeshwar , Oelke Daniela , Tremblay Chantal
Published: September 2008

In many business applications, large data workloads such as sales figures or process performance measures need to be monitored in real‐time. The data analysts want to catch problems in flight to reveal the root cause of anomalies. Immediate actions need to be taken before the problems become too expensive or consume too many resources. In the meantime, analysts need to have the “big picture” of what the information is about. In this paper, we derive and analyze two real‐time visualization techniques for managing density displays: (1) circular overlay d isplays which visualize large volumes of data without data shift movements after the display is full, thus freeing the analyst from adjusting the mental picture of the data after each data shift; and (2) variable resolution density displays which allow users to get the entire view without cluttering. We evaluate these techniques with respect to a number of evaluation measures, such as constancy of the display and usage of display space, and compare them to conventional d isplays with periodic shifts. Our real time data monitoring system also provides advanced interactions such as a local root cause analysis for further exploration. The applications using a number of real‐world data sets show the wide applicability and usefulness of our ideas.
Towards closing the analysis gap: Visual generation of decision supporting schemes from raw data
Authors: May T. , Kohlhammer J.
Published: September 2008

The derivation, manipulation and verification of analytical models from raw data is a process which requires a transformation of information across different levels of abstraction. We introduce a concept for the coupling of data classification and interactive visualization in order to make this transformation visible and steerable for the human user. Data classification techniques generate mappings that formally group data items into categories. Interactive visualization includes the user into an iterative refinement process. The user identifies and selects interesting patterns to define these categories. The following step is the transformation of a visible pattern into the formal definition of a classifier. In the last step the classifier is transformed back into a pattern that is blended with the original data in the same visual display. Our approach allows in intuitive assessment of a formal classifier and its model, the detection of outliers and the handling of noisy data using visual pattern‐matching. We instantiated the concept using decision trees for classification and KVMaps as the visualization technique. The generation of a classifier from visual patterns and its verification is transformed from a cognitive to a mostly pre‐cognitive task.
Investigative Visual Analysis of Global Terrorism
Authors: Wang Xiaoyu , Miller Erin , Smarick Kathleen , Ribarsky William , Chang Remco
Published: September 2008

Recent increases in terrorist activity around the world have made analyzing and understanding such activities more critical than ever. With the help of organizations such as the National Center for the Study of Terrorism and Responses to Terrorism (START), we now have detailed historical information on each terrorist event around the world since 1970. However, due to the size and complexity of the data, identifying terrorists' patterns and trends has been difficult. To better enable investigators in understanding terrorist activities, we propose a visual analytical system that focuses on depicting one of the most fundamental concepts in investigative analysis, the five W's (who, what, where, when, and why). Views in our system are highly correlated, and each represents one of the W's. With this approach, an investigator can interactively explore terrorist activities efficiently and discover reasons of attacks (why) by identifying patterns temporally (when), geo‐spatially (where), between multiple terrorist groups (who), and across different methods or modes of attacks (what). By coupling a global perspective with the details gleaned from asking these five questions, the system allows analysts to think both tactically and strategically.
COPERNICUS: Context‐Preserving Engine for Route Navigation with Interactive User‐modifiable Scaling
Authors: Ziegler Hartmut , Keim Daniel A.
Published: September 2008

In this paper, we present an automated system for generating context‐preserving route maps that depict navigation routes as a path between nodes and edges inside a topographic network. Our application identifies relevant context information to support navigation and orientation, and generates customizable route maps according to design principles that communicate all relevant context information clearly visible on one single page. Interactive scaling allows seamless transition between the original undistorted map and our new map design, and supports user‐specified scaling of regions of interest to create personalized driving directions according to the drivers needs.
Sound Tracing: Rendering Listener Specific Acoustic Room Properties
Authors: Bellmann Jens , Michel Frank , Deines Eduard , Hering‐Bertram Martin , Mohring Jan , Hagen Hans
Published: September 2008

We present an acoustic rendering approach visualizing the listener‐specific contribution of frequency‐dependent pressure fields on a scene geometry with acoustic reflection and scattering properties. Our method facilitates the evaluation of simulated acoustics showing the effect of simulation parameters like absorption and scattering. The image‐based spatial localization of acoustic properties is complementary to the auditive evaluation by means of auralization. Our core contribution is a pressure‐based acoustic rendering equation and a corresponding raytracing method applying techniques from photorealistic rendering to the field of simulated room acoustics. Applications are directed at the visualization of interference patterns and analyzing the impact of acoustic reflection parameters.
From Web Data to Visualization via Ontology Mapping
Authors: Gilson O. , Silva N. , Grant P.W. , Chen M.
Published: September 2008

In this paper, we propose a novel approach for automatic generation of visualizations from domain‐specific data available on the web. We describe a general system pipeline that combines ontology mapping and probabilistic reasoning techniques. With this approach, a web page is first mapped to a Domain Ontology, which stores the semantics of a specific subject domain (e.g., music charts). The Domain Ontology is then mapped to one or more Visual Representation Ontologies, each of which captures the semantics of a visualization style (e.g., tree maps). To enable the mapping between these two ontologies, we establish a Semantic Bridging Ontology, which specifies the appropriateness of each semantic bridge. Finally each Visual Representation Ontology is mapped to a visualization using an external visualization toolkit. Using this approach, we have developed a prototype software tool, SemViz, as a realisation of this approach. By interfacing its Visual Representation Ontologies with public domain software such as ILOG Discovery and Prefuse, SemViz is able to generate appropriate visualizations automatically from a large collection of popular web pages for music charts without prior knowledge of these web pages.
Lagrangian Visualization of Flow‐Embedded Surface Structures
Authors: Garth Christoph , Wiebel Alexander , Tricoche Xavier , Joy Ken , Scheuermann Gerik
Published: September 2008

The notions of Finite‐Time Lyapunov Exponent (FTLE) and Lagrangian Coherent Structures provide a strong framework for the analysis and visualization of complex technical flows. Their definition is simple and intuitive, and they are built on a deep theoretical foundation. We apply these concepts to enable the analysis of flows in the immediate vicinity of the boundaries of flow‐embedded objects by limiting the Lagrangian analysis to surfaces closely neighboring these boundaries. To this purpose, we present an approach to approximate FTLE fields over such surfaces. Furthermore, we achieve an effective depiction of boundary‐related flow structures such as separation and attachment over object boundaries and specific insight into the surrounding flow using several specifically chosen visualization techniques. We document the applicability of our methods by presenting a number of application examples.
Discrete Multi‐Material Interface Reconstruction for Volume Fraction Data
Authors: Anderson J. C. , Garth C. , Duchaineau M. A. , Joy K. I.
Published: September 2008

Material interface reconstruction (MIR) is the task of constructing boundary interfaces between regions of homogeneous material, while satisfying volume constraints, over a structured or unstructured spatial domain. In this paper, we present a discrete approach to MIR based upon optimizing the labeling of fractional volume elements within a discretization of the problem's original domain. We detail how to construct and initially label a discretization, and introduce avolume conservative swapmove for optimization. Furthermore, we discuss methods for extracting and visualizing material interfaces from the discretization. Our technique has significant advantages over previous methods: we produce interfaces between multiple materials that are continuous across cell boundaries for time‐varying and static data in arbitrary dimension with bounded error.
Topology‐Preserving λ2‐based Vortex Core Line Detection for Flow Visualization
Authors: Schafhitzel T. , Vollrath J. E. , Gois J. P. , Weiskopf D. , Castelo A. , Ertl T.
Published: September 2008

We propose a novel vortex core line extraction method based on the λ2vortex region criterion in order to improve the detection of vortex features for 3D flow visualization. The core line is defined as a curve that connects λ2minima restricted to planes that are perpendicular to the core line. The basic algorithm consists of the following stages: (1) λ2field construction and isosurface extraction; (2) computation of the curve skeleton of the λ2isosurface to build an initial prediction for the core line; (3) correction of the locations of the prediction by searching for λ2minima on planes perpendicular to the core line. In particular, we consider the topology of the vortex core lines, guaranteeing the same topology as the initial curve skeleton. Furthermore, we propose a geometry‐guided definition of vortex bifurcation, which represents the split of one core line into two parts. Finally, we introduce a user‐guided approach in order to narrow down vortical regions taking into account the graph of λ2along the computed vortex core line. We demonstrate the effectiveness of our method by comparing our results to previous core line detection methods with both simulated and experimental data; in particular, we show robustness of our method for noise‐affected data.
Illustrative Parallel Coordinates
Authors: McDonnell K. T. , Mueller K.
Published: September 2008

Illustrative parallel coordinates (IPC) is a suite of artistic rendering techniques for augmenting and improving parallel coordinate (PC) visualizations. IPC techniques can be used to convey a large amount of information about a multidimensional dataset in a small area of the screen through the following approaches: (a) edge‐bundling through splines; (b) visualization of “branched ” clusters to reveal the distribution of the data; (c) opacity‐based hints to show cluster density; (d) opacity and shading effects to illustrate local line density on the parallel axes; and (e) silhouettes, shadows and halos to help the eye distinguish between overlapping clusters. Thus, the primary goal of this work is to convey as much information as possible in a manner that is aesthetically pleasing and easy to understand for non‐experts.
Abstractive Representation and Exploration of Hierarchically Clustered Diffusion Tensor Fiber Tracts
Authors: Chen Weri , Zhang Song , Correia Stephfan , Ebert David S.
Published: September 2008

Diffusion tensor imaging (DTI) has been used to generate fibrous structures in both brain white matter and muscles. Fiber clustering groups the DTI fibers into spatially and anatomically related tracts. As an increasing number of fiber clustering methods have been recently developed, it is important to display, compare, and explore the clustering results efficiently and effectively. In this paper, we present an anatomical visualization technique that reduces the geometric complexity of the fiber tracts and emphasizes the high‐level structures. Beginning with a volumetric diffusion tensor image, we first construct a hierarchical clustering representation of the fiber bundles. These bundles are then reformulated into a 3D multi‐valued volume data. We then build a set of geometric hulls and principal fibers to approximate the shape and orientation of each fiber bundle. By simultaneously visualizing the geometric hulls, individual fibers, and other data sets such as fractional anisotropy, the overall shape of the fiber tracts are highlighted, while preserving the fibrous details. A rater with expert knowledge of white matter structure has evaluated the resulting interactive illustration and confirmed the improvement over straightforward DTI fiber tract visualization.
Hierarchical Convex Approximation of 3D Shapes for Fast Region Selection
Authors: Attene Marco , Mortara Michela , Spagnuolo Michela , Falcidieno Bianca
Published: September 2008

Given a 3D solid model S represented by a tetrahedral mesh, we describe a novel algorithm to compute a hierarchy of convex polyhedra that tightly enclose S. The hierarchy can be browsed at interactive speed on a modern PC and it is useful for implementing an intuitive feature selection paradigm for 3D editing environments. Convex parts often coincide with perceptually relevant shape components and, for their identification, existing methods rely on the boundary surface only. In contrast, we show that the notion of part concavity can be expressed and implemented more intuitively and efficiently by exploiting a tetrahedrization of the shape volume. The method proposed is completely automatic, and generates a tree of convex polyhedra in which the root is the convex hull of the whole shape, and the leaves are the tetrahedra of the input mesh. The algorithm proceeds bottom‐up by hierarchically clustering tetrahedra into nearly convex aggregations, and the whole process is significantly fast. We prove that, in the average case, for a mesh of n tetrahedra O(n log2n) operations are sufficient to compute the whole tree.
Discrete Distortion in Triangulated 3‐Manifolds
Authors: Mesmoudi Mohammed Mostefa , De Floriani Leila , Port Umberto
Published: September 2008

We introduce a novel notion, that we call discrete distortion, for a triangulated 3‐manifold. Discrete distortion naturally generalizes the notion of concentrated curvature defined for triangulated surfaces and provides a powerful tool to understand the local geometry and topology of 3‐manifolds. Discrete distortion can be viewed as a discrete approach to Ricci curvature for singular flat manifolds. We distinguish between two kinds of distortion, namely, vertex distortion, which is associated with the vertices of the tetrahedral mesh decomposing the 3‐manifold, and bond distortion, which is associated with the edges of the tetrahedral mesh. We investigate properties of vertex and bond distortions. As an example, we visualize vertex distortion on manifold hypersurfaces in R4defined by a scalar field on a 3D mesh. distance fields.
Global Intrinsic Symmetries of Shapes
Authors: Ovsjanikov Maks , Sun Jian , Guibas Leonidas
Published: September 2008

Although considerable attention in recent years has been given to the problem of symmetry detection in general shapes, few methods have been developed that aim to detect and quantify the intrinsic symmetry of a shape rather than its extrinsic, or pose‐dependent symmetry. In this paper, we present a novel approach for efficiently computing symmetries of a shape which are invariant up to isometry preserving transformations. We show that the intrinsic symmetries of a shape are transformed into the Euclidean symmetries in the signature space defined by the eigenfunctions of the Laplace‐Beltrami operator. Based on this observation, we devise an algorithm which detects and computes the isometric mappings from the shape onto itself. We show that our approach is both computationally efficient and robust with respect to small non‐isometric deformations, even if they include topological changes.
A Hierarchical Segmentation of Articulated Bodies
Authors: De Goes Fernando , Goldenstein Siome , Velho Luiz
Published: September 2008

This paper presents a novel segmentation method to assist the rigging of articulated bodies. The method computes a coarse‐to‐fine hierarchy of segments ordered by the level of detail. The results are invariant to deformations, and numerically robust to noise, irregular tessellations, and topological short‐circuits. The segmentation is based on two key ideas. First, it exploits the multiscale properties of the diffusion distance on surfaces, and then it introduces a new definition of medial structures, composing a bijection between medial structures and segments. Our method computes this bijection through a simple and fast iterative approach, and applies it to triangulated meshes.
Fast Parallel Construction of Smooth Surfaces from Meshes with Tri/Quad/Pent Facets
Authors: Myles A. , Ni T. , Peters J.
Published: September 2008

Polyhedral meshes consisting of triangles, quads, and pentagons and polar configurations cover all major sampling and modeling scenarios. We give an algorithm for efficient local, parallel conversion of such meshes to an everywhere smooth surface consisting of low‐degree polynomial pieces. Quadrilateral facets with 4‐valent vertices are ‘regular’ and are mapped to bi‐cubic patches so that adjacent bi‐cubics join C2 as for cubic tensor‐product splines. The algorithm can be implemented in the vertex and geometry shaders of the GPU pipeline and does not use the fragment shader. Its implementation in DirectX 10 achieves conversion plus rendering at 659 frames per second with 42.5 million triangles per second on input of a model of 1300 facets of which 60% are not regular.
Global Correspondence Optimization for Non‐Rigid Registration of Depth Scans
Authors: Li Hao , Sumner Robert W. , Pauly Mark
Published: September 2008

We present a registration algorithm for pairs of deforming and partial range scans that addresses the challenges of non‐rigid registration within a single non‐linear optimization. Our algorithm simultaneously solves for correspondences between points on source and target scans, confidence weights that measure the reliability of each correspondence and identify non‐overlapping areas, and a warping field that brings the source scan into alignment with the target geometry. The optimization maximizes the region of overlap and the spatial coherence of the deformation while minimizing registration error. All optimization parameters are chosen automatically; hand‐tuning is not necessary. Our method is not restricted to part‐in‐whole matching, but addresses the general problem of partial matching, and requires no explicit prior correspondences or feature points. We evaluate the performance and robustness of our method using scan data acquired by a structured light scanner and compare our method with existing non‐rigid registration algorithms.
Non‐Rigid Registration Under Isometric Deformations
Authors: Huang Qi‐Xing , Adams Bart , Wicke Martin , Guibas Leonidas J.
Published: September 2008

We present a robust and efficient algorithm for the pairwise non‐rigid registration of partially overlapping 3D surfaces. Our approach treats non‐rigid registration as an optimization problem and solves it by alternating between correspondence and deformation optimization. Assuming approximately isometric deformations, robust correspondences are generated using a pruning mechanism based on geodesic consistency. We iteratively learn an appropriate deformation discretization from the current set of correspondences and use it to update the correspondences in the next iteration. Our algorithm is able to register partially similar point clouds that undergo large deformations, in just a few seconds. We demonstrate the potential of our algorithm in various applications such as example based articulated segmentation, and shape interpolation.
Reconstructing Animated Meshes from Time‐Varying Point Clouds
Authors: Süßmuth Jochen , Winter Marco , Greiner Günther
Published: September 2008

In this paper, we describe a novel approach for the reconstruction of animated meshes from a series of time‐deforming point clouds. Given a set of unordered point clouds that have been captured by a fast 3‐D scanner, our algorithm is able to compute coherent meshes which approximate the input data at arbitrary time instances. Our method is based on the computation of an implicit function in ℝ4 that approximates the time‐space surface of the time‐varying point cloud. We then use the four‐dimensional implicit function to reconstruct a polygonal model for the first time‐step. By sliding this template mesh along the time‐space surface in an as‐rigid‐as‐possible manner, we obtain reconstructions for further time‐steps which have the same connectivity as the previously extracted mesh while recovering rigid motion exactly.

The resulting animated meshes allow accurate motion tracking of arbitrary points and are well suited for animation compression. We demonstrate the qualities of the proposed method by applying it to several data sets acquired by real‐time 3‐D scanners.
Motorcycle Graphs: Canonical Quad Mesh Partitioning
Authors: Eppstein David , Goodrich Michael T. , Kim Ethan , Tamstorf Rasmus
Published: September 2008

We describe algorithms for canonically partitioning semi‐regular quadrilateral meshes into structured submeshes, using an adaptation of the geometric motorcycle graph of Eppstein and Erickson to quad meshes. Our partitions may be used to efficiently find isomorphisms between quad meshes. In addition, they may be used as a highly compressed representation of the original mesh. These partitions can be constructed in sublinear time from a list of the extraordinary vertices in a mesh. We also study the problem of further reducing the number of submeshes in our partitions—we prove that optimizing this number is NP‐hard, but it can be efficiently approximated.
Maximum Entropy Coordinates for Arbitrary Polytopes
Authors: Hormann K. , Sukumar N.
Published: September 2008

Barycentric coordinates can be used to express any point inside a triangle as a unique convex combination of the triangle's vertices, and they provide a convenient way to linearly interpolate data that is given at the vertices of a triangle. In recent years, the ideas of barycentric coordinates and barycentric interpolation have been extended to arbitrary polygons in the plane and general polytopes in higher dimensions, which in turn has led to novel solutions in applications like mesh parameterization, image warping, and mesh deformation. In this paper we introduce a new generalization of barycentric coordinates that stems from the maximum entropy principle. The coordinates are guaranteed to be positive inside any planar polygon, can be evaluated efficiently by solving a convex optimization problem with Newton's method, and experimental evidence indicates that they are smooth inside the domain. Moreover, the construction of these coordinates can be extended to arbitrary polyhedra and higher‐dimensional polytopes.
Polyhedral Finite Elements Using Harmonic Basis Functions
Authors: Martin Sebastian , Kaufmann Peter , Botsch Mario , Wicke Martin , Gross Markus
Published: September 2008

Finite element simulations in computer graphics are typically based on tetrahedral or hexahedral elements, which enables simple and efficient implementations, but in turn requires complicated remeshing in case of topological changes or adaptive refinement. We propose a flexible finite element method for arbitrary polyhedral elements, thereby effectively avoiding the need for remeshing. Our polyhedral finite elements are based on harmonic basis functions, which satisfy all necessary conditions for FEM simulations and seamlessly generalize both linear tetrahedral and trilinear hexahedral elements. We discretize harmonic basis functions using the method of fundamental solutions, which enables their flexible computation and efficient evaluation. The versatility of our approach is demonstrated on cutting and adaptive refinement within a simulation framework for corotated linear elasticity.
Institutions and Voluntary Compliance: The Disclosure of Individual Executive Pay in Germany
Authors: Chizema Amon
Published: September 2008

Manuscript Type: Empirical

Research Question/Issue: This study seeks to understand why the disclosure of individual executive compensation, as recommended by the German Code of Corporate Governance, met with resistance in some firms while being a welcome innovation for others. Employing the theoretical perspective of institutional inertia and change, this paper identifies the characteristics of a firm likely to embrace or resist a management practice imported from an Anglo‐American system of corporate governance.

Research Findings/Results: Using data on large German firms for the years 2002 through 2005, the study shows that institutional ownership, dispersed ownership, state ownership, prior adoption of shareholder value‐oriented practices, and firm size are positively and significantly associated with the disclosure of individual executive compensation. On the other hand, the size of the supervisory board and firm age are negatively and significantly associated with individual disclosure of executive compensation.

Theoretical Implications: This study provides empirical support for the institutional inertia or change perspective at the national level for the adoption of contested management practices, taken from the Anglo‐American system and translated to the German model. As such, it adds to the argument on convergence/divergence in comparative corporate governance literature, as well as support for the neo‐institutional perspective in helping to further understand institutional change.

Practical Implications: This study offers insights to policy makers who aim to create an institutional environment that accepts corporate governance practices translated or negotiated from a different variety of capitalism. In addition, it provides a useful synthesis of the relevance and effectiveness of codes of corporate governance, thus helping policy makers to recommend continuation with the current elements of the code or to make such provisions compulsory.
Toward a Social Capital Theory of Director Selection
Authors: Kim Yangmin , Cannella Albert A.
Published: September 2008

Manuscript Type: Conceptual

Research Question/Issue: Our study evaluates the role of social capital in new director selection, board composition, and board effectiveness.

Research Findings/Insights: We take steps toward a theory of director selection, explaining how social capital at the individual‐level influences director selection and at the group level influences board effectiveness. At the individual level, social capital is defined as the interpersonal linkages that director candidates have to others, both inside and outside the firm. At the group level, board social capital is an asset that includes both relations of directors and potential resources arising from the relations.

Theoretical/Academic Implications: We argue that: 1) social capital can be divided into internal and external dimensions according to its locus and function; 2) both internal and external social capital are associated with board composition through director selection, although the causal logic differs considerably; 3) the influences of social capital on director selection vary according to the context; and 4) both internal social capital and external social capital generate unique resources that are important to board effectiveness.

Practitioner/Policy Implications: Our study informs practicing managers, because we describe how and why most research and public discussion has emphasized the role of directors as monitors of managers and this has significantly downplayed the role of directors in providing advice, counsel, and other resources to their organizations. We provide a strong logic for seeking directors with specific types of social capital (internal or external) under specific contexts.
Kernel Likelihood Inference for Time Series
Authors: GRILLENZONI CARLO
Published: September 2008

Abstract.  This paper develops non‐parametric techniques for dynamic models whose data have unknown probability distributions. Point estimators are obtained from the maximization of a semiparametric likelihood function built on the kernel density of the disturbances. This approach can also provide Kullback–Leibler cross‐validation estimates of the bandwidth of the kernel densities. Confidence regions are derived from the dual‐empirical likelihood method based on non‐parametric estimates of the scores. Limit theorems for martingale difference sequences support the statistical theory; moreover, simulation experiments and a real case study show the validity of the methods.