Wolfgang Müller

CD and NMR Studies of Prion Protein (PrP) Helix 1 NOVEL IMPLICATIONS FOR ITS ROLE IN THE PrPC→ PrPSc CONVERSION PROCESS

The conversion of prion helix 1 from an α-helical into an extended conformation is generally assumed to be an essential step in the conversion of the cellular isoform PrPC of the prion protein to the pathogenic isoform PrPSc. Peptides encompassing helix 1 and flanking sequences were analyzed by nuclear magnetic resonance and circular dichroism. Our results indicate a remarkably high instrinsic helix propensity of the helix 1 region. In particular, these peptides retain significant helicity under a wide range of conditions, such as high salt, pH variation, and presence of organic co-solvents. As evidenced by a data base search, the pattern of charged residues present in helix 1 generally favors helical structures over alternative conformations. Because of its high stability against environmental changes, helix 1 is unlikely to be involved in the initial steps of the pathogenic conformational change. Our results implicate that interconversion of helix 1 is rather representing a barrier than a nucleus for the PrPC→ PrPSc conversion.

Fast retrieval of high-dimensional feature vectors in P2P networks using compact peer data summaries

The retrieval facilities of most Peer-to-Peer (P2P) systems are limited to queries based on a unique identifier or a small set of keywords. The techniques used for this purpose are hardly applicable for content-based image retrieval (CBIR) in a P2P network. Furthermore, we will argue that the curse of dimensionality and the high communication overhead prevent the adaptation of multidimensional search trees or fast sequential scan techniques for P2P CBIR. In the present paper we will propose two compact data representations which can be distributed in a P2P network and used as the basis for a source selection. This allows to communicate only with a small fraction of all peers during query processing without deteriorating the result quality significantly. We will also present experimental results confirming our approach.

Efficient content-based P2P image retrieval using peer content descriptions

Peer-to-peer (P2P) networks are overlay networks that connect independent computers (also called nodes or peers). In contrast to client/server solutions, all nodes offer and request services from other peers in a P2P network. P2P networks are very attractive in that they harness the computing power of many common desktop machines and necessitate little administrative overhead. While the resulting computing power is impressive, efficiently looking up data still is the major challenge in P2P networks. Current work comprises fast lookup of one-dimensional values (Distributed Hash Tables, DHT) and retrieval of texts using few keywords. However, the lookup of multimedia data in P2P networks is still attacked by very few groups. In this paper, we present experiments with efficient Content Based Image Retrieval in a P2P environment, thus a P2P-CBIR system. The challenge in such systems is to limit the number of messages sent, and to maximize the usefulness of each peer contacted in the query process. We achieve this by distributing peer data summaries over the network. Obviously, the data summaries have to be compact in order to limit the communication overhead. We propose an CBIR scheme based on a compact peer data summary. This peer data summary relies on cluster frequencies. To obtain the compact representation of a peers collection, a global clustering of the data is efficiently calculated in a distributed manner. After that, each peer publishes how many of its images fall into each cluster. These cluster frequencies are then used by the querying peer to contact only those peers that have the largest number of images present in one cluster given by the query. In our paper we further detail the various challenges that have to be met by the designers of such a P2P-CBIR, and we present experiments with varying degree of data replication (duplicates of images), as well as quality of clustering within the network.

Faster Exact Histogram Intersection on Large Data Collections Using Inverted VA-Files

Most indexing structures for high-dimensional vectors used in multimedia retrieval today rely on determining the importance of each vector component at indexing time in order to create the index. However for Histogram Intersection and other important distance measures this is not possible because the importance of vector components depends on the query. We present an indexing structure inspired by VA-file and Inverted file that does not need to determine the importance at indexing time in order to perform well. Instead, our structure adapts to the importance of vector components at query processing time.

Picadomo: Faceted Image Browsing for Mobile Devices

Picadomo combines content-based image retrieval and faceted search on mobile devices. It is designed for finding images with desired visual properties, tags or other known metadata. Due to the limitations of mobile devices such as small screen sizes and low processing power, we had to carefully select the features that come in use (dominant color, GPS data, tags, etc.). With Picadomo the user can pick visualized facets directly via touch screen, while using very little screen size for the facet browsing navigation. We present our architecture, the facets used for image browsing, our new control concept and user experiments.

CLUSTERING-BASED, LOAD BALANCED SOURCE SELECTION FOR CBIR IN P2P NETWORKS

In peer-to-peer (P2P) networks, computers with equal rights form a logical (overlay) network in order to provide a common service that lies beyond the capacity of every single participant. Efficient similarity search is generally recognized as a frontier in research about P2P systems. One way to address this issue is using data source selection based approaches where peers summarize the data they contribute to the network, generating typically one summary per peer. When processing queries, these summaries are used to choose the peers (data sources) that are most likely to contribute to the query result. Only those data sources are contacted. There are several contributions of this article. We extend earlier work, adding a data source selection method for high-dimensional vector data, comparing different peer ranking schemes. Furthermore, we present two methods that use progressive stepwise data exchange between peers to better each peers summary and therefore improve the systems performance. We finally examine the effect of these data exchange methods with respect to load balancing.

Reducing I/O Cost of Similarity Queries by Processing Several at a Time

Current research on high-dimensional indexing structures for multimedia retrieval is focused on obtaining optimal performance for single k-NN queries. Within this paper, we argue for parallel processing of multiple nearest neighbor queries. This is beneficial when there is heavy load on the server and efficiency is important. We argue that query performance for parallel queries is an important parameter in the evaluation of the usefulness of indexing structures. We show that by processing multiple queries simultaneously we can dramatically reduce the cost of each single query involved. We support these findings via experiments on VA- and inverted VA-files, an improved variant of VA-files.

Semi pandiagonal magic 4 × 4-squares

It is proved that the set of all semi pandiagonal 4 × 4-squares precisely consists of 3456 squares belonging to three orbits under the faithful action of a group of order 1152 which is a semi direct product of symmetric groups.

Halbeinfache Moduln und Ringe

In diesem Paragraphen werden jene Hilfsmittel aus der Theorie der halbeinfachen Moduln und Ringe bereitgestellt, die in der gewohnlichen Darstellungstheorie von Bedeutung sind.

Relativ-projektive Moduln

In diesem Paragraphen sei K ein Korper, G eine endliche Gruppe und KG die zugehorige Gruppenalgebra. Da die im folgenden in Anlehnung an Hamernik [ 8 ] entwickelte Theorie nur dann von Bedeutung ist, wenn char K /IGI, sei zusatzlich gefordert: char K = p > 0.