Self-destructive percolation

Consider ordinary site percolation on an infinite graph in which the sites, independent of each other, are occupied with probability $p$ and vacant with probability $1-p$. Now suppose that, by some `catastrophe', all sites which are in an infinite occupied cluster become vacant. Finally, each vacant site gets an extra enhancement to become occupied. More precisely, each site that was already vacant or that was made vacant by the catastrophe, becomes occupied with probability $delta$ (independent of the other sites). When $p$ is larger than but close to the critical value $p_c$ one might believe (for `nice' graphs) that only a small $delta$ is needed to have an infinite occupied cluster in the final configuration. This appears to be indeed the case for the binary tree. However, on the square lattice we strongly conjecture that this is not true. We discuss the background for these problems and also show that the conjecture, if true, has some remarkable consequences

Biomedical colonialism or local autonomy?: local healers in the fight against tuberculosis

Analiza el papel de los agentes médicos autóctonos y sus conocimientos en las campañas antituberculosas contemporáneas en el África subsahariana. Sitúa la medicina contemporánea, llevada a cabo en África en la herencia cultural de la medicina colonial, para comprender el marco histórico en el que se desarrollaron, a partir de los años setenta del siglo XX, las estrategias de la Organización Mundial de la Salud de promoción y desarrollo de las medicinas 'tradicionales'. En los proyectos sanitarios analizados, se evalúan las prácticas médicas locales y se entrenan a los agentes autóctonos para integrarlos en actividades estrictamente biomédicas: identificación de síntomas, remisión a hospitales o supervisión de tratamientos farmacológicos.The article explores the role played by indigenous medical agents, and their knowledge, within contemporary tuberculosis campaigns in sub-Saharan Africa. To understand the historical framework within which the World Health Organization devised its strategies to promote and develop traditional medicine as of the 1970s, the article contextualizes contemporary medicine as a cultural legacy of colonial medicine. Under the public healthcare projects analyzed in the article, local medical practices were assessed and indigenous agents trained so they could take part in strictly biomedical activities, like symptom identification, referrals to hospitals, or supervision of drug treatments.Trabajo realizado para la obtención del Diploma de Estudios Avanzados (DEA) en el programa de doctorado Salud: Antropología e Historia, bajo la dirección de la profesora Rosa María Medina Doménech

ENIGMA and global neuroscience: A decade of large-scale studies of the brain in health and disease across more than 40 countries

This review summarizes the last decade of work by the ENIGMA (Enhancing NeuroImaging Genetics through Meta Analysis) Consortium, a global alliance of over 1400 scientists across 43 countries, studying the human brain in health and disease. Building on large-scale genetic studies that discovered the first robustly replicated genetic loci associated with brain metrics, ENIGMA has diversified into over 50 working groups (WGs), pooling worldwide data and expertise to answer fundamental questions in neuroscience, psychiatry, neurology, and genetics. Most ENIGMA WGs focus on specific psychiatric and neurological conditions, other WGs study normal variation due to sex and gender differences, or development and aging; still other WGs develop methodological pipelines and tools to facilitate harmonized analyses of "big data" (i.e., genetic and epigenetic data, multimodal MRI, and electroencephalography data). These international efforts have yielded the largest neuroimaging studies to date in schizophrenia, bipolar disorder, major depressive disorder, post-traumatic stress disorder, substance use disorders, obsessive-compulsive disorder, attention-deficit/hyperactivity disorder, autism spectrum disorders, epilepsy, and 22q11.2 deletion syndrome. More recent ENIGMA WGs have formed to study anxiety disorders, suicidal thoughts and behavior, sleep and insomnia, eating disorders, irritability, brain injury, antisocial personality and conduct disorder, and dissociative identity disorder. Here, we summarize the first decade of ENIGMA's activities and ongoing projects, and describe the successes and challenges encountered along the way. We highlight the advantages of collaborative large-scale coordinated data analyses for testing reproducibility and robustness of findings, offering the opportunity to identify brain systems involved in clinical syndromes across diverse samples and associated genetic, environmental, demographic, cognitive, and psychosocial factors

Novel genetic loci associated with hippocampal volume

The hippocampal formation is a brain structure integrally involved in episodic memory, spatial navigation, cognition and stress responsiveness. Structural abnormalities in hippocampal volume and shape are found in several common neuropsychiatric disorders. To identify the genetic underpinnings of hippocampal structure here we perform a genome-wide association study (GWAS) of 33,536 individuals and discover six independent loci significantly associated with hippocampal volume, four of them novel. Of the novel loci, three lie within genes (ASTN2, DPP4 and MAST4) and one is found 200 kb upstream of SHH. A hippocampal subfield analysis shows that a locus within the MSRB3 gene shows evidence of a localized effect along the dentate gyrus, subiculum, CA1 and fissure. Further, we show that genetic variants associated with decreased hippocampal volume are also associated with increased risk for Alzheimer's disease (rg =-0.155). Our findings suggest novel biological pathways through which human genetic variation influences hippocampal volume and risk for neuropsychiatric illness

Box-crossings and continuity results for self-destructive percolation in the plane

A few years ago (see [1]) two of us introduced, motivated by the study of certain forest-fire processes, the self-destructive percolation model (abbreviated as sdp model). A typical configuration for the sdp model with parameters p and δ is generated in three steps: First we generate a typical configuration for the ordinary site percolation model with parameter p. Next, we make all sites in the infinite occupied cluster vacant. Finally, each site that was already vacant in the beginning or made vacant by the above action, becomes occupied with probability δ (independent of the other sites). Let ϕ(p,δ) be the probability that some specified vertex belongs, in the final configuration, to an infinite occupied cluster. In our earlier paper we stated the conjecture that, for the square lattice and other planar lattices, the function ϕ(·,·) has a discontinuity at points of the form (p,δ), with δ sufficiently small. We also showed (see [2]) remarkable consequences for the forest-fire models. The conjecture naturally raises the question whether the function ϕ(·,·) is continuous outside some region of the above-mentioned form. We prove that this is indeed the case. An important ingredient in our proof is a somewhat modified (improved) form of a recent RSW-like (box-crossing) result of Bollobás and Riordan ([4]). We believe that this modification is also useful for many other percolation models

Box-crossings and continuity results for self-destructive percolation in the plane

A few years ago (see [1]) two of us introduced, motivated by the study of certain forest-fire processes, the self-destructive percolation model (abbreviated as sdp model). A typical configuration for the sdp model with parameters p and δ is generated in three steps: First we generate a typical configuration for the ordinary site percolation model with parameter p. Next, we make all sites in the infinite occupied cluster vacant. Finally, each site that was already vacant in the beginning or made vacant by the above action, becomes occupied with probability δ (independent of the other sites). Let ϕ(p,δ) be the probability that some specified vertex belongs, in the final configuration, to an infinite occupied cluster. In our earlier paper we stated the conjecture that, for the square lattice and other planar lattices, the function ϕ(·,·) has a discontinuity at points of the form (p,δ), with δ sufficiently small. We also showed (see [2]) remarkable consequences for the forest-fire models. The conjecture naturally raises the question whether the function ϕ(·,·) is continuous outside some region of the above-mentioned form. We prove that this is indeed the case. An important ingredient in our proof is a somewhat modified (improved) form of a recent RSW-like (box-crossing) result of Bollobás and Riordan ([4]). We believe that this modification is also useful for many other percolation models