Sergei Startchik

The intercellular synchronization of Ca2+ oscillations evaluates Cx36-dependent coupling.

Connexin36 (Cx36) plays an important role in insulin secretion by controlling the intercellular synchronization of Ca2+ transients induced during stimulation. The lack of drugs acting on Cx36 channels is a major limitation in further unraveling the molecular mechanism underlying this effect. To screen for such drugs, we have developed an assay allowing for a semi-automatic, fluorimetric quantification of Ca2+ transients in large populations of MIN6 cells. Here, we show that (1) compared to control cells, MIN6 cells with reduced Cx36 expression or function showed decreased synchrony of glucose-induced Ca2+ oscillations; (2) glibenclamide, a sulphonylurea which promotes Cx36 junctions and coupling, increased the number of synchronous MIN6 cells, whereas quinine, an antimalarial drug which inhibits Cx36-dependent coupling, decreased this proportion; (3) several drugs were identified that altered the intercellular Ca2+ synchronization, cell coupling and distribution of Cx36; (4) some of them also affected insulin content. The data indicate that the intercellular synchronization of Ca2+ oscillations provides a reliable and non-invasive measurement of Cx36-dependent coupling, which is useful to identify novel drugs affecting the function of β-cells, neurons, and neuron-related cells that express Cx36.

Archival and retrieval of historical watermark images

This project concerns the management of a multimedia database (text and image) of historical papers representing ancient watermarks. The current database contains roughly 3000 images of such watermarks; the system allows archival and retrieval by means of textual or morphological criteria. During the archival phase, textual description are stored, as well as descriptive primitives extracted together with the watermark itself by image analysis methods. For the retrieval phase, several types of queries are supported; they allow textual search on the basis of the accompanying descriptions, morphological search according to global characteristics, and shape based search on the basis of the watermark shape.

Projective and Illumination Invariant Representation of Disjoint Shapes

A projectively invariant representation for groups of planar disjoint contours is proposed as a simultaneous polar reparametrization of multiple curves. Its origin is an invariant point and for each ray orientation, the cross-ratio of the intersections with its closest curves is taken as a value associated to the radius. The sequence of cross-ratio values for all orientations represents a signature. With respect to other methods this representation is less reliant on single curve properties, both for the construction of the projective basis and for calculating the signature. The proposed representation has been originally developed for planar shapes, but an extension is proposed and validated for trihedral corners. Illumination invariant measures are introduced into the representation to increase it discrimination capability. The whole approach is applied to shape-based retrieval from image databases. Experiments are reported on a database of real trademarks.

Projective and illumination invariant representation of disjoint shapes

We describe a projectively invariant representation of disjoint contour groups, which is suitable for shape-based retrieval from an image database. It consists of simultaneous polar reparametrization of multiple curves where an invariant point is used as the origin. For each ray orientation, a cross-ratio of its intersections with other curves is taken as a value associated to the radius. With respect to other methods, this representation is less reliant on single curve properties, both for the construction of the projective basis and for calculating the signature. It is, therefore, more robust to contour gaps and image noise and is better suited to describing complex planar shapes defined by multiple disjoint curves. Moreover, we show that illumination invariance fits well within the proposed framework and can easily be introduced in the representation in order to make it more appropriate for shape-based retrieval. Experiments are reported on a database of real trademarks.

Tangible interactive system for document browsing and visualisation of multimedia data

In this paper we introduce and develop a framework for document interactive navigation in multimodal databases. First, we analyze the main open issues of existing multimodal interfaces and then discuss two applications that include interaction with documents in several human environments, i.e., the so-called smart rooms. Second, we propose a system set-up dedicated to the efficient navigation in the printed documents. This set-up is based on the fusion of data from several modalities that include images and text. Both modalities can be used as cover data for hidden indexes using data-hiding technologies as well as source data for robust visual hashing. The particularities of the proposed robust visual hashing are described in the paper. Finally, we address two practical applications of smart rooms for tourism and education and demonstrate the advantages of the proposed solution.