29 research outputs found
Force transmission in migrating cells
No full textDuring cell migration, forces generated by the actin cytoskeleton are transmitted through adhesion complexes to the substrate. To investigate the mechanism of force generation and transmission, we analyzed the relationship between actin network velocity and traction forces at the substrate in a model system of persistently migrating fish epidermal keratocytes. Front and lateral sides of the cell exhibited much stronger coupling between actin motion and traction forces than the trailing cell body. Further analysis of the traction - velocity relationship suggested that the force transmission mechanisms were different in different cell regions: at the front, traction was generated by a gripping of the actin network to the substrate, whereas at the sides and back, it was produced by the network's slipping over the substrate. Treatment with inhibitors of the actin - myosin system demonstrated that the cell body translocation could be powered by either of the two different processes, actomyosin contraction or actin assembly, with the former associated with significantly larger traction forces than the latter. © 2010 Fournier et al.LC
Emergent properties of electrically coupled smooth muscle cells
No full textAsynchronous and synchronous calcium oscillations occur in a variety of cells. A well-established pathway for intercellular communication is provided by gap junctions which connect adjacent cells and can mediate electrical and chemical coupling. Several experimental studies report that cells presenting only a transient increase when freshly dispersed may oscillate when they are coupled. Such observations suggest that the role of gap junctions is not only to coordinate calcium oscillations of adjacent cells. Gap junctions may also be important to generate oscillations. Here we illustrate the emergent properties of electrically coupled smooth muscle cells using a model that we recently proposed. A bifurcation analysis in the case of two cells reveals that synchronous and asynchronous calcium oscillations can be induced by electrical coupling. In a larger population of smooth muscle cells, electrical coupling may result in the creation of groups of cells presenting synchronous calcium oscillations. The elements of one group may be distant from each other. Moreover, our results highlight a general mechanism by which gap junctional electrical coupling can give rise to out of phase calcium oscillations in smooth muscle cells that are non-oscillating when uncoupled. All these observations remain true in the case of non-identical cells, except that the solution corresponding to synchronous calcium oscillations disappears and that the formation of groups is sensitive to the degree of heterogeneit
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A Multi-Methodology Study of the Historic Impact of Soft Systems Methodology and Its Associated Data Visualization Approach in the Context of Operations and Business Strategy
No full textThe purpose of this three-essay dissertation was to expand knowledge and theory regarding soft systems methodologies (SSMs) and data visualization approaches in business, engineering, and other social sciences. The first essay depicts a bibliometric analysis study of the historic impacts of SSM from 1980-2018 on business, engineering, and other social sciences fields. This study found 285 articles that described or employed SSM for research and included outcomes such as top SSM authors, author citation impacts, common dissemination outlets, time-bound distribution of publications, and other relevant findings. This study provided a picture of who, what, why, when, and where SSM has had the greatest impact on academic thought and practice. The second essay presents research on the academic impact of Systemigrams, an associated data visualization approach, finding examples of conceptual or research development that employed Systemigrams to depict complex problem situations. Recommendations for improvement of designing these data visualizations to increase their field use resulted from this study. The final essay leverages a selection of the articles as use cases to produce a grounded theory study to identify phenomena that arose from the use of SSM for operations and firm strategy research. This study identified two broad themes including (i) scope, structure, and process challenges and (ii) performance and evaluation limitations. These themes were explained by six patterns that emerged from the publications. Each produced change recommendations for SSM process, practice, and reporting to support its continued viability and adoption in business and operations research
M-theory on : new facts from a careful analysis
No full text32 pages, version to appear in Nucl. Phys. B, no figures, uses PHYZZXInternational audienceWe carefully re-examine the issues of solving the modified Bianchi identity, anomaly cancellations and flux quantization in the S^1/Z_2 orbifold of M-theory using the boundary-free "upstairs" formalism, avoiding several misconceptions present in earlier literature. While the solution for the four-form G to the modified Bianchi identity appears to depend on an arbitrary parameter b, we show that requiring G to be globally well-defined, i.e. invariant under small and large gauge and local Lorentz transformations, fixes b=1. This value also is necessary for a consistent reduction to the heterotic string in the small-radius limit. Insisting on properly defining all fields on the circle, we find that there is a previously unnoticed additional contribution to the anomaly inflow from the eleven-dimensional topological term. Anomaly cancellation then requires a quadratic relation between b and the combination lambda^6/kappa^4 of the gauge and gravitational coupling constants lambda and kappa. This contrasts with previous beliefs that anomaly cancellation would give a cubic equation for b. We observe that our solution for G automatically satisfies integer or half-integer flux quantization for the appropriate cycles. We explicitly write out the anomaly cancelling terms of the heterotic string as inherited from the M-theory approach. They differ from the usual ones by the addition of a well-defined local counterterm. We also show how five-branes enter our analysis
Effects of Arterial Wall Stress on Vasomotion
No full textAbstractSmooth muscle and endothelial cells in the arterial wall are exposed to mechanical stress. Indeed blood flow induces intraluminal pressure variations and shear stress. An increase in pressure may induce a vessel contraction, a phenomenon known as the myogenic response. Many muscular vessels present vasomotion, i.e., rhythmic diameter oscillations caused by synchronous cytosolic calcium oscillations of the smooth muscle cells. Vasomotion has been shown to be modulated by pressure changes. To get a better understanding of the effect of stress and in particular pressure on vasomotion, we propose a model of a blood vessel describing the calcium dynamics in a coupled population of smooth muscle cells and endothelial cells and the consequent vessel diameter variations. We show that a rise in pressure increases the calcium concentration. This may either induce or abolish vasomotion, or increase its frequency depending on the initial conditions. In our model the myogenic response is less pronounced for large arteries than for small arteries and occurs at higher values of pressure if the wall thickness is increased. Our results are in agreement with experimental observations concerning a broad range of vessels
A Bibliographic and Visual Exploration of the Historic Impact of Soft Systems Methodology on Academic Research and Theory
No full textSoft systems methodology (SSM), an analytic method commonly employed in engineering and business research, produces models focused on human activities and relevant structures used to explain complex, engineered systems. The original version of SSM involves seven stages; five address real-world aspects and observable data, while two stages leverage a systems thinking viewpoint. This approach allows the development of a simplified depiction of complex systems representative of the multi-perspective lenses used to comprehend the systemic complexity of a problem and provide a clearer picture to analysts and decision makers. This bibliometric meta-analysis of 286 relevant publications in engineering, business, and other social sciences fields explores the historic impacts of SSM on academic research and systems thinking in relevant publications that described or employed SSM for research from 1980⁻2018. This study produced descriptive narrative outcomes and data visualizations including information about top SSM authors, author citation impacts, common dissemination outlets for SSM work, and other relevant metrics commonly used to measure academic impact. The goal of this piece is to depict who, what, why, when, and where SSM had the greatest impact on research, systems thinking, and methodology after nearly 40 years of use, as we look towards its future as a methodological approach used to comprehend complex problem situations
Role of the Endothelium on Arterial Vasomotion
No full textAbstractIt is well-known that cyclic variations of the vascular diameter, a phenomenon called vasomotion, are induced by synchronous calcium oscillations of smooth muscle cells (SMCs). However, the role of the endothelium on vasomotion is unclear. Some experimental studies claim that the endothelium is necessary for synchronization and vasomotion, whereas others report rhythmic contractions in the absence of an intact endothelium. Moreover, endothelium-derived factors have been shown to abolish vasomotion by desynchronizing the calcium signals in SMCs. By modeling the calcium dynamics of a population of SMCs coupled to a population of endothelial cells, we analyze the effects of an SMC vasoconstrictor stimulation on endothelial cells and the feedback of endothelium-derived factors. Our results show that the endothelium essentially decreases the SMCs calcium level and may move the SMCs from a steady state to an oscillatory domain, and vice versa. In the oscillatory domain, a population of coupled SMCs exhibits synchronous calcium oscillations. Outside the oscillatory domain, the coupled SMCs present only irregular calcium flashings arising from noise modeling stochastic opening of channels. Our findings provide explanations for the published contradictory experimental observations
