Descripción: A mathematical setting, for a method of fractal block-coding of image functions was presented. The method was based on the notion of generalized self-similarity model. Block-coding techniques along with this functional model allowed, to take advantage of local redundancy of the images. It was shown that the generalized self-similarity model could be used for the coding and reconstruction of digital signals and images.

Descripción: This paper presents the results of the application of terrestrial magnetometry in the study of waste deposits. The area chosen for the pilot study was located toward the south of the town of Gualeguaychú, in the southeastern Entre Rios province. This location was selected because it was known that operations were to cease and local authorities had an interest in verifying the presence of anomalies indicative of potentially dangerous environmental pollutants. Interpretation of the magnetic signal suggests that buried objects of high magnetic susceptibility are not large (smaller than containers of 1m in height). For that reason we discount the presence of drums of standard dimensions, the possible containers of toxic elements. The estimated depth of the objects of high susceptibility increases with the distance from the access road to the the area. © 2004 Asociación Geológica Argentina.

Descripción: Calcium signals participate in a large variety of physiological processes. In many instances, they involve calcium entry through inositol 1,4,5-trisphosphate (IP3) receptors (IP3Rs), which are usually organized in clusters. Recent high-resolution optical experiments by Smith & Parker have provided new information on Ca2+ release from clustered IP3Rs. In the present paper, we use the model recently introduced by Solovey & Ponce Dawson to determine how the distribution of the number of IP3Rs that become open during a localized release event may change by the presence of Ca2+ buffers, substances that react with Ca2+, altering its concentration and transport properties. We then discuss how buffer properties could be extracted from the observation of local signals. © 2010 The Royal Society.

Descripción: The spontaneous non-obese diabetic (NOD) mouse model of Sjögren's syndrome provides a valuable tool to study the onset and progression of both the autoimmune response and secretory dysfunction. Our purpose was to analyse the temporal decline of salivary secretion in NOD mice in relation to the autoimmune response and alterations in various signalling pathways involved in saliva secretion within each salivary gland. A progressive loss of nitric oxide synthase activity in submandibular and parotid glands started at 12 weeks of age and paralleled the decline in salivary secretion. This defect was associated with a lower response to vasoactive intestinal peptide in salivary flow rate, cAMP and nitric oxide/cGMP production. No signs of mononuclear infiltrates or local cytokine production were detectable in salivary glands in the time period studied (10-16 weeks of age). Our data support a disease model for sialadenitis in NOD mice in which the early stages are characterized by defective neurotransmitter-mediated signalling in major salivary glands that precedes the autoimmune response. © 2005 British Society for Immunology.

Descripción: Calcium signals are involved in a large variety of physiological processes. Their versatility relies on the diversity of spatiotemporal behaviors that the calcium concentration can display. Calcium entry through inositol 1,4,5-trisphosphate (IP3) receptors (IP3R's) is a key component that participates in both local signals such as "puffs" and in global waves. IP3R's are usually organized in clusters on the membrane of the endoplasmic reticulum and their spatial distribution has important effects on the resulting signal. Recent high resolution observations [1] of Ca2+ puffs offer a window to study intra-cluster organization. The experiments give the distribution of the number of IP3R's that open during each puff without much processing. Here we present a simple model with which we interpret the experimental distribution in terms of two stochastic processes: IP3 binding and unbinding and Ca2+-mediated inter-channel coupling. Depending on the parameters of the system, the distribution may be dominated by one or the other process. The transition between both extreme cases is similar to a percolation process. We show how, from an analysis of the experimental distribution, information can be obtained on the relative weight of the two processes. The largest distance over which Ca2+mediated coupling acts and the density of IP3-bound IP3R's of the cluster can also be estimated. The approach allows us to infer properties of the interactions among the channels of the cluster from statistical information on their emergent collective behavior. © 2010 Solovey, Dawson.