Informatik und Informationswissenschaft
Auflistung nach
Neueste Zugänge
-
graf_212815.pdf (1.235Mb)Graf, Sebastian; Rain, Andreas; Waldvogel, Marcel (2013), Working Paper / Technical Report[more][less]
Zusammenfassung: Being a part of any social network becomes a necessity especially for the sake of self-presentation. Specialized social networks like LinkedIn are aware of these needs and offer tailored functionalities like referencing to relevant projects and topics including specific searching functionalities. Since the social data stored within any centralized social network represents an alluring mass of information, security and privacy concerns come up within their utilization. As a consequence, guidelines for their usage are deployed within institutions to increase awareness related to these concerns. Unfortunately, the specific toolsets deployed within universities for presenting users and projects support neither the sharing of group-based or public information nor the ability to create social connections between users especially not over the borders of single institutions. To combine the need of self-presentation with the ability of virtual social interaction, we present a prototype of a federated, distributed, social network tailored to the need of researchers. Our prototype is based on Diaspora, representing the largest distributed social platform nowadays. Enriched with automated, user-related profiles, our Diaspora-pod offers all members of the University of Konstanz the ability to interact in combination with automated university-profiles. Tightly integrated in the existing infrastructure of the University of Konstanz and hosted on trusted infrastructure, the described prototype offers not only user-defined sharing of personal profiles in a federated way. It also leverages from the centralized handling of profiles and reduces as a consequence the administrative overhead of maintaining any personal information. Based on its simple usage and the tight integration into the services of the University of Konstanz, our prototype has the potential to push university life to a new social level without generating concerns about security and privacy. Dateien zu dieser Publikation: 1
graf_212815.pdf (1.235Mb) -
Neubert, Boris (München : Dr. Hut, 2013), Dissertation[more][less]
Zusammenfassung: This thesis presents new methods for modeling and efficient rendering of botanical scenes and objects. The first method allows for producing 3D tree models from a set of images with limited user intervention by combining principles of image- and simulation-based modeling techniques. This technique meets two important criteria improving common modeling techniques: it is possible to achieve a high visual similarity to photographs and at the same time allows for simple manipulation of the resulting plant by altering the input photographs and changing the shape or density, providing the artist with an expressive tool while leveraging the need for manual modeling plant details.<br /><br /> The second method improves the concept of sketch-based modeling tools for plants. The proposed system converts a freehand sketch of a tree drawn by the user into a full 3D model that is both, complex and realistic-looking. This is achieved by probabilistic optimization based on parameters obtained from a database of tree models. Branch interaction is modeled by a Markov random field, to inferring missing information of the tree structure and combining sketch-based and data-driven methodologies. Both modeling methods presented in this book, produce very complex tree models. While this richness is needed to model highly realistic scenes, it leads to a complexity that makes real-time rendering impossible. We present an optimized pruning algorithm that allows for considerable geometry reduction in large botanical scenes, while maintaining high and coherent rendering quality. We improve upon previous techniques by applying model-specific geometry reduction functions and optimized scaling functions. To optimize the improvement, we propose the use of Precision and Recall (PR) as a measure of quality to rendering and show how PR-scores can be used to predict better scaling values. Finally, we extend the originally purely stochastic geometry prioritization for pruning in order to account for a view-optimized geometry selection, which allows taking global scene information, such as occlusion, into consideration. We demonstrate our method for rendering of scenes with thousands of complex tree models in real-time. Dateien zu dieser Publikation: 0
-
Kuhnt, Daniela; Bauer, Miriam H.A.; Egger, Jan; Richter, Mirco; Kapur, Tina; Sommer, Jens; Merhof, Dorit; Nimsky, Christopher (2013), Artikel[more][less]
Erschienen in: Neurosurgery ; 72 (2013), Suppl. 1. - S. A165-A175 Zusammenfassung: Background: The most frequently used method for fiber tractography based on diffusion tensor imaging (DTI) is associated with restrictions in the resolution of crossing or kissing fibers and in the vicinity of tumor or edema. Tractography based on high-angular-resolution diffusion imaging (HARDI) is capable of overcoming this restriction. With compressed sensing (CS) techniques, HARDI acquisitions with a smaller number of directional measurements can be used, thus enabling the use of HARDI-based fiber tractography in clinical practice. Objective: To investigate whether HARDI+CS-based fiber tractography improves the display of neuroanatomically complex pathways and in areas of disturbed diffusion properties. Methods: Six patients with gliomas in the vicinity of language-related areas underwent 3-T magnetic resonance imaging including a diffusion-weighted data set with 30 gradient directions. Additionally, functional magnetic resonance imaging for cortical language sites was obtained. Fiber tractography was performed with deterministic streamline algorithms based on DTI using 3 different software platforms. Additionally, tractography based on reconstructed diffusion signals using HARDI+CS was performed. Results: HARDI+CS-based tractography displayed more compact fiber bundles compared with the DTI-based results in all cases. In 3 cases, neuroanatomically plausible fiber bundles were displayed in the vicinity of tumor and peritumoral edema, which could not be traced on the basis of DTI. The curvature around the sylvian fissure was displayed properly in 6 cases and in only 2 cases with DTI-based tractography. Conclusion: HARDI+CS seems to be a promising approach for fiber tractography in clinical practice for neuroanatomically complex fiber pathways and in areas of disturbed diffusion, overcoming the problem of long acquisition times. Dateien zu dieser Publikation: 0
-
Graf, Sebastian; Lang, Patrick; Hohenadel, Stefan; Waldvogel, Marcel (2013), Konferenzveröffentlichung[more][less]
Erschienen in: Proceedings : 2012 31st international Symposium on Reliable Distributed Systems ;; SRDS 2012 ; 8-11 October 2012, Irvine, California, USA / Ed. prod. Juan E. Guerrero. - Piscataway : IEEE, 2012. - S. 469-474. - ISBN 978-0-7695-4784 Zusammenfassung: Not only does storing data in the cloud utilize specialized infrastructures facilitating immense scalability and high availability, but it also offers a convenient way to share any information with user-defined third-parties. However, storing data on the infrastructure of commercial third party providers, demands trust and confidence. Simple approaches, like merely encrypting the data by providing encryption keys, which at most consist of a shared secret supporting rudimentary data sharing, do not support evolving sets of accessing clients to common data. Based on approaches from the area of stream-encryption, we propose an adaption for enabling scalable and flexible key management within heterogeneous environments like cloud scenarios. Representing access-rights as a graph, we distinguish between the keys used for encrypting hierarchical data and the encrypted updates on the keys enabling flexible join-/leave-operations of clients. This distinction allows us to utilize the high availability of the cloud as updating mechanism without harming confidentiality. Our graph-based key management results in an adaption of nodes related to the changed key. The updates on the keys again continuously create an overhead related to the number of these updated nodes. The proposed scalable approach utilizes cloud-based infrastructures for confidential data and key sharing in collaborative workflows supporting variable client-sets. Dateien zu dieser Publikation: 0
-
richter_224078.pdf (1.249Mb)Richter, Mirco; Zolal, Amir; Ganslandt, Oliver; Buchfelder, Michael; Nimsky, Christopher; Merhof, Dorit (2013), Artikel[more][less]
Erschienen in: PLoS ONE ; 8 (2013), 1. - e50132 Zusammenfassung: Pre-operative planning and intra-operative guidance in neurosurgery require detailed information about the location of functional areas and their anatomo-functional connectivity. In particular, regarding the language system, post-operative deficits such as aphasia can be avoided. By combining functional magnetic resonance imaging and diffusion tensor imaging, the connectivity between functional areas can be reconstructed by tractography techniques that need to cope with limitations such as limited resolution and low anisotropic diffusion close to functional areas. Tumors pose particular challenges because of edema, displacement effects on brain tissue and infiltration of white matter. Under these conditions, standard fiber tracking methods reconstruct pathways of insufficient quality. Therefore, robust global or probabilistic approaches are required. In this study, two commonly used standard fiber tracking algorithms, streamline propagation and tensor deflection, were compared with a previously published global search, Gibbs tracking and a connection-oriented probabilistic tractography approach. All methods were applied to reconstruct neuronal pathways of the language system of patients undergoing brain tumor surgery, and control subjects. Connections between Broca and Wernicke areas via the arcuate fasciculus (AF) and the inferior fronto-occipital fasciculus (IFOF) were validated by a clinical expert to ensure anatomical feasibility, and compared using distance- and diffusion-based similarity metrics to evaluate their agreement on pathway locations. For both patients and controls, a strong agreement between all methods was observed regarding the location of the AF. In case of the IFOF however, standard fiber tracking and Gibbs tracking predominantly identified the inferior longitudinal fasciculus that plays a secondary role in semantic language processing. In contrast, global search resolved connections in almost every case via the IFOF which could be confirmed by probabilistic fiber tracking. The results show that regarding the language system, our global search is superior to clinically applied conventional fiber tracking strategies with results similar to time-consuming global or probabilistic approaches. Dateien zu dieser Publikation: 1
richter_224078.pdf (1.249Mb) -
Richter, Mirco; Merhof, Dorit (2013), Konferenzveröffentlichung[more][less]
Erschienen in: Bildverarbeitung für die Medizin 2013 : Algorithmen - Systeme - Anwendungen. Proceedings des Workshops vom 3. bis 5. März 2013 in Heidelberg / Hans-Peter Meinzer ... - Berlin : Springer, 2013. - S. 33-38. - ISBN 978-3-642-36479-2 Zusammenfassung: In several studies, brain atrophy measured by cortical thickness has shown to be a meaningful biomarker for Alzheimer’s disease. In this research field, the level of granularity at which values are compared is an important aspect. Vertex- and voxel-based approaches can detect atrophy at a very fine scale, but are susceptible to noise from misregistrations and inter-subject differences in the population. Regional approaches are more robust to these kinds of noise, but cannot detect variances at a local scale. In this work, an optimized classifier is presented for a parcellation scheme that provides a trade-off between both paradigms by increasing the granularity of a regional approach. For this purpose, atlas regions are subdivided into gyral and sulcal parts at different height levels. Using two-stage feature selection, optimal gyral and sulcal subregions are determined for the final classification with sparse logistic regression. The robustness was assessed on clinical data by 10- fold cross-validation and by testing the prediction accuracy for unseen individuals. In every aspect, superior classification performance was observed as compared to the original parcellation scheme which can be explained by the increased locality of cortical thickness measures and the customized classification approach that reveals interacting regions. Dateien zu dieser Publikation: 0
-
Zhang, Xinpeng (2013), Artikel[more][less]
Erschienen in: IEEE Transactions on Multimedia ; 15 (2013), 2. - S. 316-325 Zusammenfassung: In reversible data hiding techniques, the values of host data are modified according to some particular rules and the original host content can be perfectly restored after extraction of the hidden data on receiver side. In this paper, the optimal rule of value modification under a payload-distortion criterion is found by using an iterative procedure, and a practical reversible data hiding scheme is proposed. The secret data, as well as the auxiliary information used for content recovery, are carried by the differences between the original pixel-values and the corresponding values estimated from the neighbors. Here, the estimation errors are modified according to the optimal value transfer rule. Also, the host image is divided into a number of pixel subsets and the auxiliary information of a subset is always embedded into the estimation errors in the next subset. A receiver can successfully extract the embedded secret data and recover the original content in the subsets with an inverse order. This way, a good reversible data hiding performance is achieved. Dateien zu dieser Publikation: 0
-
Graf_234273.pdf (701.2Kb)Graf, Sebastian; Miller, Wolfgang; Waldvogel, Marcel (2013), Working Paper / Technical Report[more][less]
Zusammenfassung: Cloud Storage stands for cheap storage and unprecedented ubiquitous availability. The optimal choice of cloud storage provider and model is not simple, given the many charging models available. Photo sharing websites such as Facebook, Picasa-Web, and Flickr provide very attractive cloud storage, if pictures are all you need to store. Obviously pictures can be used to store information in, which has been used for steganography and watermarking at low data rates. We propose a general framework for storing large amounts of data, its data density and error-correcting mechanisms tunable to the properties of the photo sharing website of your choice. Our cost-performance-analysis shows that photo sharing websites compare favorably to professional cloud storage services such as Amazon S3. Thanks to the integration of our software as a backend to the widely-used jClouds framework, everyone can now use photo sharing websites as one component for low-cost purposes, including archival. Dateien zu dieser Publikation: 1
Graf_234273.pdf (701.2Kb) -
Shen, Minmin; Zimmer, Bastian; Leist, Marcel; Merhof, Dorit (2013), Konferenzveröffentlichung[more][less]
Erschienen in: Bildverarbeitung für die Medizin 2013 : Algorithmen - Systeme - Anwendungen. Proceedings des Workshops vom 3. bis 5. März 2013 in Heidelberg / Hans-Peter Mainzer ... - Berlin : Springer, 2013. - S. 152-157. - ISBN 978-3-642-36479-2 Zusammenfassung: Methods to evaluate migration capacity of stem cells and the inhibition by chemicals are important for biomedical research. Here, we established an automated image processing framework to quantify migration of human neural crest (NC) cells into an initially empty, circular region of interest (ROI). The ROI is partially filled during the experiment by migrating cells. Based on an image captured only once at the end of the biological experiment, the framework identifies the initial ROI. The identification worked also, when the distribution of surrounding cells showed large heterogeneity. After segmentation, the number of migrated cells was identified. The image processing framework was capable of efficiently quantifying chemical effects on cell migration. Dateien zu dieser Publikation: 0
-
leitner_fischer_233165.pdf (8.227Mb)Leitner-Fischer, Florian; Leue, Stefan (2013), Konferenzveröffentlichung[more][less]
Erschienen in: Verification, Model Checking, and Abstract Interpretation : 14th International Conference, VMCAI 2013, Rome, Italy, January 20-22, 2013, Proceedings / ed. by Roberto Giacobazzi ... - Berlin : Springer, 2013. - S. 248-267. - (Lecture Notes in Computer Science ; 7737). - ISBN 978-3-642-35872-2 Zusammenfassung: We present an approach for the algorithmic computation of causalities in system models that we refer to as causality checking. We base our notion of causality on counterfactual reasoning, in particular using the structural equation model approach by Halpern and Pearl that we recently have extended to reason about computational models. In this paper we present a search-based on-the-fly approach that nicely integrates into finite state verification techniques, such as explicit-state model checking. We demonstrate the applicability of our approach using an industrial case study. Dateien zu dieser Publikation: 1
leitner_fischer_233165.pdf (8.227Mb)
