1,720,957 research outputs found
Mathematical modelling of brain tumour growth. Integrating mechanics, phenotypic evolution, and nutrient transport to describe anisotropic behaviour and personalised therapies.
Full text linkL'abstract è presente nell'allegato / the abstract is in the attachmen
Modelling and simulation of anisotropic growth in brain tumours through poroelasticity: A study of ventricular compression and therapeutic protocols
Full text linkMalignant brain tumours represent a significant medical challenge due to their aggressive nature and unpredictable locations. The growth of a brain tumour can result in a mass effect, causing compression and displacement of the surrounding healthy brain tissue and possibly leading to severe neurological complications. In this paper, we propose a multiphase mechanical model for brain tumour growth that quantifies deformations and solid stresses caused by the expanding tumour mass and incorporates anisotropic growth influenced by brain fibres. We employ a sharp interface model to simulate localised, non-invasive solid brain tumours, which are those responsible for substantial mechanical impact on the surrounding healthy tissue. By using patient-specific imaging data, we create realistic three-dimensional brain geometries and accurately represent ventricular shapes, to evaluate how the growing mass may compress and deform the cerebral ventricles. Another relevant feature of our model is the ability to simulate therapeutic protocols, facilitating the evaluation of treatment efficacy and guiding the development of personalized therapies for individual patients. Overall, our model allows to make a step towards a deeper analysis of the complex interactions between brain tumours and their environment, with a particular focus on the impact of a growing cancer on healthy tissue, ventricular compression, and therapeutic treatment
Effective macroscopic equations for biological fluid and nutrients' transport in vascularized tumors growing via proliferation and chemotaxis
Full text linkThis paper presents a system of partial differential equations designed to model fluid and nutrient transport within the growing tumor microenvironment. The fluid phase, representing both cells and extracellular fluids flowing within the interstitial space, is assumed to be intrinsically incompressible, so that growth can be modeled as a source, generally defined by volumetric growth terms and nonconvective mass fluxes. Specifically, we consider the volumetric growth term proportional to the nutrient concentration and the nonconvective mass flux driven by the nutrient gradient. By exploiting the scale separation between the microscopic vascular structures and the larger tumor tissue, we employ asymptotic homogenization to derive effective macroscopic equations that integrate detailed microscale characteristics. The resulting model operates as a double porous medium framework, where fluid dynamics are driven by both pressure and concentration gradient, which reduces to a more standard Darcy's law when microscale variations of the convective mass flux are neglected. Nutrient transport is captured through a coupled advection–diffusion–reaction system. Permeability and diffusivity tensors, which encapsulate the influence of microvascular geometry, are computed via cell-problem analysis to accurately reflect the microscale structure within the macroscopic model. Given that the tissue model includes a fluid phase that continually exchanges with the surrounding vasculature, along with nutrients, the Kedem–Katchalsky formulation is employed to represent fluid and nutrient transport across the capillary walls. This approach provides valuable insights into the interactions between vascular architecture and tumor growth. Although certain limitations remain, such as the static tumor domain and assumptions regarding cell proliferation, the framework offers a foundation for further development. It is adaptable for numerical simulations based on real tumor geometries, with promising potential to inform and improve anticancer treatment strategies through the integration of patient-specific clinical data
Modelling the non-linear viscoelastic behaviour of brain tissue in torsion
Full text linkBrain tissue accommodates non-linear deformations and exhibits time-dependent mechanical behaviour. The latter is one of the most pronounced features of brain tissue, manifesting itself primarily through viscoelastic effects such as stress relaxation. To investigate its viscoelastic behaviour, we performed ramp-and-hold relaxation tests in torsion on freshly slaughtered cylindrical ovine brain samples (25 mm diameter and ∼10 mm height). The tests were conducted using a commercial rheometer at varying twist rates of {40, 240, 400} rad m−1 s−1, with the twist remaining fixed at ∼88 rad m−1, which generated two independent datasets for torque and normal force. The complete set of viscoelastic material parameters was estimated via a simultaneous fit to the analytical expressions for the torque and normal force predicted by the modified quasi-linear viscoelastic model. The model's predictions were further validated through finite element simulations in FEniCS. Our results show that the modified quasi-linear viscoelastic model—recently reappraised and largely unexploited—accurately fits the experimental data. Moreover, the estimated material parameters are in line with those obtained in previous studies on brain samples under torsion. These material parameters could enhance our understanding of slow-progressing pathologies such as tumour growth or neurodegeneration and inform the development of improved in silico models for brain surgery planning and training. Our novel testing protocol also offers an efficient, robust and reliable method for determining the viscoelastic properties of brain tissue under much more rapid loading conditions, which are of crucial importance for modelling traumatic brain injury.This publication has emanated from research jointly funded by Taighde Éireann – Research Ireland under grant number GOIPG/2024/3552 (Griffen Small), and by the College of Science and Engineering at the University of Galway under the Millennium Fund scheme for the project “Modelling Brain Mechanics” (Valentina Balbi). Francesca Ballatore acknowledges support from the PNRR M4C2 through the project “Made in Italy Circolare e Sostenibile (MICS)”, CUP: E13C22001900001. The authors are grateful to the anonymous reviewers for their constructive criticisms, helpful suggestions and insights.peer-reviewe
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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