Control of brain blood flow by capillaries: a simulation study in an anatomically accurate large human vascular network

In this paper, the variations in cerebral blood flow induced by global or localised capillary vasodilations are studied. The results demonstrate that pericyte-mediated regulation of blood flowat capillary level would be efficient for neuro-vascular coupling. By contrast to a regulation situated at the level of arterioles (Lorthois et al. 2011b), the changes in blood volume can be highly localised in space, with the potential to be as close as possible of areas of neuronal activation. However, the changes in blood flow are much more diffuse. This imposes limits on the ultimate spatial resolution of hemodynamically based brain functional imaging techniques

Goldstone Bosons in Josephson Junctions

For a microscopic model of a Josephson junction the normal coordinates of the two junction Goldstone bosons are constructed and their dynamical spectrum is computed. The explicit dependence on the phase difference of the two superconductors is calculated

Self-consistent equation for an interacting Bose gas

We consider interacting Bose gas in thermal equilibrium assuming a positive and bounded pair potential $V(r)$ such that 0<\int d\br V(r) = a<\infty. Expressing the partition function by the Feynman-Kac functional integral yields a classical-like polymer representation of the quantum gas. With Mayer graph summation techniques, we demonstrate the existence of a self-consistent relation $\rho (\mu)=F(\mu-a\rho(\mu))$ between the density $\rho$ and the chemical potential $\mu$, valid in the range of convergence of Mayer series. The function $F$ is equal to the sum of all rooted multiply connected graphs. Using Kac's scaling V_{\gamma}(\br)=\gamma^{3}V(\gamma r) we prove that in the mean-field limit $\gamma\to 0$ only tree diagrams contribute and function $F$ reduces to the free gas density. We also investigate how to extend the validity of the self-consistent relation beyond the convergence radius of Mayer series (vicinity of Bose-Einstein condensation) and study dominant corrections to mean field. At lowest order, the form of function $F$ is shown to depend on single polymer partition function for which we derive lower and upper bounds and on the resummation of ring diagrams which can be analytically performed.Comment: 33 pages, 6 figures, submitted to Phys.Rev.

Cognitive mapping of organic vegetable production in Flanders to support farmers strategy design

Organic farmers inherently have to cope with complex agricultural production system processes. Next to pursuing economic performance, farm management also encompasses optimization of the farm's ecological and social performance. The question arises how to maintain a certain balance between the multiple purposes. For this consideration, farmers as well as researchers need to have a good understanding of the whole farm functioning. Therefore this study aims to model the factors and their inter-relations influencing an organic farmers' decision-making process. These factors and inter-relations were modelled by using the qualitative cognitive mapping technique. Cognitive mapping can be used to develop maps of socio-ecological systems based on people's knowledge of ecosystems. Different stakeholders (farmers and experts) were interviewed in order to represent and visualize their tacit knowledge. Through in-depth interviews, stakeholders were questioned on the critical success factors of organic farm management and how these factors relate to each other. Based on these interviews, individual cognitive maps were constructed which were subsequently merged to build a social cognitive map. The social cognitive map represents the stakeholders' perception of the agricultural production system. It covers a broad range of factors (economic, agro-technical and biophysical factors, next to a few social factors), of which the most central ones are crop choice, crop rotation, marketing and technology and mechanization

Image-Guided Biopsy in the Esophagus through Comprehensive Optical Frequency Domain Imaging and Laser Marking: A Study in Living Swine

Background: Random biopsy esophageal surveillance can be subject to sampling errors, resulting in diagnostic uncertainty. Optical frequency domain imaging (OFDI) is a high-speed, 3-dimensional endoscopic microscopy technique. When deployed through a balloon-centering catheter, OFDI can automatically image the entire distal esophagus (6.0 cm length) in approximately 2 minutes. Objective: To test a new platform for guided biopsy that allows the operator to select target regions of interest on an OFDI dataset, and then use a laser to mark the esophagus at corresponding locations. The specific goals include determining the optimal laser parameters, testing the accuracy of the laser marking process, evaluating the endoscopic visibility of the laser marks, and assessing the amount of mucosal damage produced by the laser. Design: Experimental study conducted in 5 swine in vivo. Setting: Massachusetts General Hospital. Main Outcome Measurements: Success rate, including endoscopic visibility of laser marks and accuracy of the laser marking process for selected target sites, and extent of the thermal damage caused by the laser marks. Results: All of the laser-induced marks were visible by endoscopy. Target locations were correctly marked with a success rate of 97.07% (95% confidence interval, 89.8%-99.7%). Thermal damage was limited to the superficial layers of the mucosa and was observed to partially heal within 2 days. Limitations: An animal study with artificially placed targets to simulate pathology. Conclusions: The study demonstrates that laser marking of esophageal sites identified in comprehensive OFDI datasets is feasible and can be performed with sufficient accuracy, precision, and visibility to guide biopsy in vivo