1,720,983 research outputs found
Vortices Termination in the Cardiac Muscle
No full textMethods for termination of three-dimensional electrical vortices in the heart are needed for development of patient-friendly cardiac defibrillation techniques (Nature 475, 235, 2011). The defibrillation technique used today is the delivery of a high-energy electric shock (360 J, 1 kV, 30 A, 12 ms, when applied externally) often associated with severe side effects. Developing low-energy defibrillation methods are hampered by two problems: the unknown locations of the cores of the vortices, and the unpredictable phases of the vortex waves rotating around these cores. The first problem has been resolved through the use of electric field pulses to excite the cores of all pinned vortices simultaneously. Approaches to solve the second problem are being developed. One of them is based on the phase scanning of all pinned vortices in parallel to hit the critical time window (“Vulnerable Window”, VW) of every pinned vortex. We investigate the related physical mechanisms and describe problems created by scanning. We describe also a mechanism by which a 3-dim scroll vortex may be terminated with a VW of the full 2π radians. It makes knowledge of the wave phase no longer required. We describe a mechanism terminating also a free (not pinned) vortex, when the vortex’s core passes not very far from a defect. About 500 experiments with termination of vortices during ventricular fibrillation in pig isolated hearts confirm that pinned vortices, hidden from direct observation, are significant in fibrillation. These results form a physical basis needed for creation of new effective methods for termination vortices underlying fibrillation
Reverse-engineering biological networks from large data sets
Full text linkMuch of contemporary systems biology owes its success to the abstraction of a network, the idea that diverse kinds of molecular, cellular, and organismal species and interactions can be modeled as relational nodes and edges in a graph of dependencies. Since the advent of high-throughput data-acquisition technologies in fields such as genomics, metabolomics, and neuroscience, the automated inference and reconstruction of such interaction networks directly from large sets of activation data, commonly known as reverse-engineering, has become a routine procedure. Whereas early attempts at network reverse-engineering focused predominantly on producing maps of system architectures with minimal predictive modeling, reconstructions now play instrumental roles in answering questions about the statistics and dynamics of the underlying systems they represent. Many of these predictions have clinical relevance, suggesting novel paradigms for drug discovery and disease treatment. While other reviews focus predominantly on the details and effectiveness of individual network inference algorithms, here we examine the emerging field as a whole. We first summarize several key application areas in which inferred networks have made successful predictions. We then outline the two major classes of reverse-engineering methodologies, emphasizing that the type of prediction that one aims to make dictates the algorithms one should employ. We conclude by discussing whether recent breakthroughs justify the computational costs of large-scale reverse-engineering sufficiently to admit it as a mainstay in the quantitative analysis of living systems.Fil: Natale, Joseph J.. University of Emory; Estados UnidosFil: Hofmann, David. University of Emory; Estados UnidosFil: Hernández Lahme, Damián Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. University of Emory; Estados UnidosFil: Nemenman, Ilya. University of Emory; Estados Unido
Recommended from our members
Modeling for Process Control: High-Dimensional Systems
Full text linkMost of other technologically important systems (among them, powders and other granular systems) are intrinsically nonlinear. This project is focused on building the dynamical models for granular systems as a prototype for nonlinear high-dimensional systems exhibiting complex non-equilibrium phenomena. Granular materials present a unique opportunity to study these issues in a technologically important and yet fundamentally interesting setting. Granular systems exhibit a rich variety of regimes from gas-like to solid-like depending on the external excitation. Based the combination of the rigorous asymptotic analysis, available experimental data and nonlinear signal processing tools, we developed a multi-scale approach to the modeling of granular systems from detailed description of grain-grain interaction on a micro-scale to continuous modeling of large-scale granular flows with important geophysical applications
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
Statistical Theory of Asymmetric Damage Segregation in Clonal Cell Populations
Full text linkAsymmetric damage segregation (ADS) is ubiquitous among unicellular
organisms: After a mother cell divides, its two daughter cells receive
sometimes slightly, sometimes strongly different fractions of damaged proteins
accumulated in the mother cell. Previous studies demonstrated that ADS provides
a selective advantage over symmetrically dividing cells by rejuvenating and
perpetuating the population as a whole. In this work we focus on the
statistical properties of damage in individual lineages and the overall damage
distributions in growing populations for a variety of ADS models with different
rules governing damage accumulation, segregation, and the lifetime dependence
on damage. We show that for a large class of deterministic ADS rules the
trajectories of damage along the lineages are chaotic, and the distributions of
damage in cells born at a given time asymptotically becomes fractal. By
exploiting the analogy of linear ADS models with the Iterated Function Systems
known in chaos theory, we derive the Frobenius-Perron equation for the
stationary damage density distribution and analytically compute the damage
distribution moments and fractal dimensions. We also investigate nonlinear and
stochastic variants of ADS models and show the robustness of the salient
features of the damage distributions.Comment: Mathematical Biosciences, 2023 (in press
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
- …
