196,271 research outputs found
Physical modelling and simulations of tumour growth and angiogenesis: predictions and new hypotheses
No full textThe initial stages of tumour growth (avascular phase) are characterised by a low nutrient availability, which soon become a limiting factor for the progression of the neoplasm. Normally a transition to a vascular phase occurs, during which cancer cells stimulate the proliferation of endothelial cells belonging to vessels, hence the formation of new capillaries. The newly formed vascular system rapidly approaches the tumour surface and even infiltrates it, providing additional nutrients which allow further growth (angiogenesis). Blocking the process, might induce tumour to latency, with the consequent implications from therapeutical point of view. In the present contribution we will consider angiogenesis as a case study to show how mathematical models help in the interpretation and quantification of the experimental results
Modelling the coupling between apoptosis and host rigidity in the growth of Multicellular Tumor Spheroids
No full textEnvironmental physical modulation of intrinsic tendency to growth of Multicellular Tumour Spheroids: in silico experiments
No full textLowering in nutrient local availability and rising in host mechanical rigidity are two distinct boundary conditions that affect the growth of solid a-vascular cancers in similar ways (inhibition of growth). In silico experiments based on a physical-mathematical model can shed light on some of the mechanisms at the basis of these effects and suggest that the self-organizing properties of neoplastic populations are greatly modulated by environmental restrictions
Robustness of computational time reversal imaging in media with elastic constant uncertainties
No full textIn order to image a source or a scatterer embedded in a three dimensional solid, acoustic/elastic wave data from an actual experiment are time reversed and backpropagated through a numerical model of the medium. The model makes use of estimates for the elastic constants of the laboratory solid. These estimates may not be very precise, for example, due to experimental uncertainties. Poor characterization of the medium leads to the degradation of the time reversal focus, therefore, to poor medium imaging. In this work, we report on the results of investigating the time reversal focus degradation as the estimates depart from the real values. Very small deviations from the medium's actual elastic constants degrade the time reversal focus dramatically. However, decreasing the total duration of the signals used for time reversal can attenuate the degradation in some cases. We propose a new method to compensate for the deviations of the model medium's elastic constants from the actual values. Finally, we explore the effects of scatterers that may exist in the laboratory medium, but are not included in the model medium, and show that their presence does not produce significant effects on the time reversal focu
Nonlinear elastic response of thermally damaged consolidated granular media
No full textThe mechanical properties of consolidated granular media are strongly affected by large temperature changes which induce the development and localization of stresses, leading in turn to damage, e.g., cracking. In this work, we study the evolution of linear and nonlinear elasticity parameters when increasing the temperature of the thermal loading process. We prove the existence of a link between linear and nonlinear elasticity properties. We show that the change of the nonlinear elasticity parameters with the increase in the thermal loading is larger at the lower temperatures than the corresponding change for the linear parameters, suggesting that nonlinear elasticity can be exploited for early thermal damage detection and characterization in consolidated granular media. We finally show the influence of grain size upon the thermal damage evolution with the loading temperature and how this evolution is mirrored by the nonlinear elasticity parameter
Modeling the growth of multicellular tumor spheroids: role of medium rigidity, cell adhesion and apoptosis
No full textNumerical analysis of the anomalous elastic behavior of hysteretic media: quasi-static, dynamic and relaxation experiments
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Transport Properties in the Adriatic Sea as deduced from Drifter Data
No full textThe surface transport properties in the Adriatic Sea, a semienclosed subbasin of the Mediterranean Sea, have been studied using a drifter dataset in the period December 1994-March 1996. Three main points have been addressed. First, the exchange between southern and northern regions and between deep and coastal areas have been studied, focusing on the role of topography. A significant cross-topography or cross-shelf exchange has been found, probably due to the direct wind forcing and to the influence of stratification that isolates the surface flow from bottom effects, especially in the open sea. Second, a Lagrangian transport model with parameters derived from the data has been implemented. Simulated particles have been compared with drifter data with positive results. The model is found to be able to reproduce reality with good approximation, except for a specific advective event during the late summer season. Finally, the residence timescale T, that is, the average time spent by a surface particle in the basin, has been estimated. Direct estimates from the data suggest T ~ 70-90 days, but these values are biased due to the finite lifetime of the drifters. Model results have been used to estimate the bias, and they suggest a 'true' value of T ~ 200 day
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