Fundamentación y utilización de aproximaciones clásicas en colisiones de iones con átomos

Esta tesis trata sobre los procesos de ionización y capturaelectrónica que ocurren como consecuencia de la colisión de union positivo pesado con un blanco formado por un núcleo pesado yun electrón activo. En el presente trabajo describiremos estosfenómenos mediante aproximaciones totalmente clásicas: losiones pesados proyectil y núcleo blanco son tratados comopartículas clásicas, mientras que la función de onda asociada alelectrón activo es tratada como un fluido clásico. Se presenta una conexión original entre algunasaproximaciones clásicas de la teoría de colisiones y la mecánicacuántica. Esta conexión está basada en la interpretaciónhidrodinámica de la función de onda cuántica. Se precisan lasaproximaciones cuánticas que conducen a una formulaciónsemiclásica de los modelos de Thomson y Monte Carlo detrayectorias clásicas y se definen las funciones de ondaasociadas a los mismos. Se hace una discusión acerca de losprocedimientos que pueden ser utilizados para calcular seccioneseficaces de dispersión. Se muestra que, si se integra laamplitud de transición por unidad de tiempo, se obtiene elcorrecto comportamiento de las secciones eficaces a altasenergías de colisión. También se presenta la implementación numérica del método Monte Carlo de trayectorias clásicas. Se muestran distintasdistribuciones iniciales que pueden utilizarse y se deducen,dentro del formalismo de la ecuación de Liouville, las leyes deescala asociadas a las secciones eficaces clásicas. Se indicacómo tomar muestras representativas de cada una de las posiblesdistribuciones iniciales a ser utilizadas. El método Monte Carlo de trayectorias clásicas es utilizadopara estudiar distintos sistemas colisionantes. Se presentansecciones eficaces totales de ionización y captura electrónicapara colisiones de iones multicargados con blancos de H(1s), He+(1s) y H(2s) y se discute el rango de validez del método. Semuestra que, contrariamente a lo que predice la primeraaproximación de Born, las secciones eficaces totales ysimplemente diferenciales de ionización y excitación no aumentanindefinidamente con la carga del proyectil y se investiga lasaturación de las mismas. También se estudian los sistemas H(+) + He y H(+) + Li(+), los cuales involucran blancos de doselectrones, representando las interacciones mediante potencialesmodelo y dentro del formalismo de electrones independientes. Entodos los casos se obtiene un buen acuerdo con otros modelosteóricos y/o datos experimentales, salvo para la dobleionización de He.This thesis deals with the ionization and electron-captureprocesses that take place as a consecuence of the collisionbetween a heavy positive ion and a target consisting in a heavynucleus and an active electron. Completely classicalapproximations are used to describe these processes: theprojectile and target-nucleus heavy ions are considered to beclassical particles, while the wavefunction associated to theactive electron is treated as a classical fluid. A connection between quantum mechanics and some classicalapproximations is presented. This connection is based on thefluid-dynamical interpretation of the quantum wavefunction. Theclassical trajectory Monte Carlo and Thomson methods are derivedas suitable approximations in a quantum mechanical formalism andthe associated wavefunctions are defined. A discussion is madeabout the procedure to be used to calculate scattering crosssections. It is shown that if the transition amplitude per unittime is integrated, the correct behaviour of the cross sectionsat high collision energies is obtained. The numerical implementation of the classical trajectory Monte Carlo method is also presented. Different initialdistributions that may be used are shown and the scaling lawsassociated with the classical cross sections are deduced withinthe Liouville equation formalism. The way to sample initialconditions representing different initial distributions is alsoshown. The classical trajectory Monte Carlo method is employed tostudy different collision systems. Total ionisation and capturecross sections for fully stripped ions colliding with H(1s), He+(1s) and H(2s) targets are presented and the validity rangeof the classical approximation is discussed. It is shown that,contrarily to the predictions of the first Born approximation,total and single differential ionization and excitation crosssections are bound when the projectile charge is increased. Thesaturation of those cross sections is investigated. The systems H(+) + He and H(+) + Li(+), which involve two-electron targets, are alsostudied by representing the interactions with model potentialsand within the independent-electron formalism. Good agreementis found with other theoretical approximations and/orexperimental data, except for double ionization of He.Fil: Reinhold Larsson, Carlos Oscar. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Fundamentación y utilización de aproximaciones clásicas en colisiones de iones con átomos

Esta tesis trata sobre los procesos de ionización y capturaelectrónica que ocurren como consecuencia de la colisión de union positivo pesado con un blanco formado por un núcleo pesado yun electrón activo. En el presente trabajo describiremos estosfenómenos mediante aproximaciones totalmente clásicas: losiones pesados proyectil y núcleo blanco son tratados comopartículas clásicas, mientras que la función de onda asociada alelectrón activo es tratada como un fluido clásico. Se presenta una conexión original entre algunasaproximaciones clásicas de la teoría de colisiones y la mecánicacuántica. Esta conexión está basada en la interpretaciónhidrodinámica de la función de onda cuántica. Se precisan lasaproximaciones cuánticas que conducen a una formulaciónsemiclásica de los modelos de Thomson y Monte Carlo detrayectorias clásicas y se definen las funciones de ondaasociadas a los mismos. Se hace una discusión acerca de losprocedimientos que pueden ser utilizados para calcular seccioneseficaces de dispersión. Se muestra que, si se integra laamplitud de transición por unidad de tiempo, se obtiene elcorrecto comportamiento de las secciones eficaces a altasenergías de colisión. También se presenta la implementación numérica del método Monte Carlo de trayectorias clásicas. Se muestran distintasdistribuciones iniciales que pueden utilizarse y se deducen,dentro del formalismo de la ecuación de Liouville, las leyes deescala asociadas a las secciones eficaces clásicas. Se indicacómo tomar muestras representativas de cada una de las posiblesdistribuciones iniciales a ser utilizadas. El método Monte Carlo de trayectorias clásicas es utilizadopara estudiar distintos sistemas colisionantes. Se presentansecciones eficaces totales de ionización y captura electrónicapara colisiones de iones multicargados con blancos de H(1s), He+(1s) y H(2s) y se discute el rango de validez del método. Semuestra que, contrariamente a lo que predice la primeraaproximación de Born, las secciones eficaces totales ysimplemente diferenciales de ionización y excitación no aumentanindefinidamente con la carga del proyectil y se investiga lasaturación de las mismas. También se estudian los sistemas H(+) + He y H(+) + Li(+), los cuales involucran blancos de doselectrones, representando las interacciones mediante potencialesmodelo y dentro del formalismo de electrones independientes. Entodos los casos se obtiene un buen acuerdo con otros modelosteóricos y/o datos experimentales, salvo para la dobleionización de He.This thesis deals with the ionization and electron-captureprocesses that take place as a consecuence of the collisionbetween a heavy positive ion and a target consisting in a heavynucleus and an active electron. Completely classicalapproximations are used to describe these processes: theprojectile and target-nucleus heavy ions are considered to beclassical particles, while the wavefunction associated to theactive electron is treated as a classical fluid. A connection between quantum mechanics and some classicalapproximations is presented. This connection is based on thefluid-dynamical interpretation of the quantum wavefunction. Theclassical trajectory Monte Carlo and Thomson methods are derivedas suitable approximations in a quantum mechanical formalism andthe associated wavefunctions are defined. A discussion is madeabout the procedure to be used to calculate scattering crosssections. It is shown that if the transition amplitude per unittime is integrated, the correct behaviour of the cross sectionsat high collision energies is obtained. The numerical implementation of the classical trajectory Monte Carlo method is also presented. Different initialdistributions that may be used are shown and the scaling lawsassociated with the classical cross sections are deduced withinthe Liouville equation formalism. The way to sample initialconditions representing different initial distributions is alsoshown. The classical trajectory Monte Carlo method is employed tostudy different collision systems. Total ionisation and capturecross sections for fully stripped ions colliding with H(1s), He+(1s) and H(2s) targets are presented and the validity rangeof the classical approximation is discussed. It is shown that,contrarily to the predictions of the first Born approximation,total and single differential ionization and excitation crosssections are bound when the projectile charge is increased. Thesaturation of those cross sections is investigated. The systems H(+) + He and H(+) + Li(+), which involve two-electron targets, are alsostudied by representing the interactions with model potentialsand within the independent-electron formalism. Good agreementis found with other theoretical approximations and/orexperimental data, except for double ionization of He.Fil: Reinhold Larsson, Carlos Oscar. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Serum magnesium and calcium levels in relation to ischemic stroke: Mendelian randomization study

ObjectiveTo determine whether serum magnesium and calcium concentrations are causally associated with ischemic stroke or any of its subtypes using the mendelian randomization approach.MethodsAnalyses were conducted using summary statistics data for 13 single-nucleotide polymorphisms robustly associated with serum magnesium (n = 6) or serum calcium (n = 7) concentrations. The corresponding data for ischemic stroke were obtained from the MEGASTROKE consortium (34,217 cases and 404,630 noncases).ResultsIn standard mendelian randomization analysis, the odds ratios for each 0.1 mmol/L (about 1 SD) increase in genetically predicted serum magnesium concentrations were 0.78 (95% confidence interval [CI] 0.69-0.89; p = 1.3 × 10-4) for all ischemic stroke, 0.63 (95% CI 0.50-0.80; p = 1.6 × 10-4) for cardioembolic stroke, and 0.60 (95% CI 0.44-0.82; p = 0.001) for large artery stroke; there was no association with small vessel stroke (odds ratio 0.90, 95% CI 0.67-1.20; p = 0.46). Only the association with cardioembolic stroke was robust in sensitivity analyses. There was no association of genetically predicted serum calcium concentrations with all ischemic stroke (per 0.5 mg/dL [about 1 SD] increase in serum calcium: odds ratio 1.03, 95% CI 0.88-1.21) or with any subtype.ConclusionsThis study found that genetically higher serum magnesium concentrations are associated with a reduced risk of cardioembolic stroke but found no significant association of genetically higher serum calcium concentrations with any ischemic stroke subtype

Meta-analysis of 74,046 individuals identifies 11 new susceptibility loci for Alzheimer's disease

Eleven susceptibility loci for late-onset Alzheimer's disease (LOAD) were identified by previous studies; however, a large portion of the genetic risk for this disease remains unexplained. We conducted a large, two-stage meta-analysis of genome-wide association studies (GWAS) in individuals of European ancestry. In stage 1, we used genotyped and imputed data (7,055,881 SNPs) to perform meta-analysis on 4 previously published GWAS data sets consisting of 17,008 Alzheimer's disease cases and 37,154 controls. In stage 2, 11,632 SNPs were genotyped and tested for association in an independent set of 8,572 Alzheimer's disease cases and 11,312 controls. In addition to the APOE locus (encoding apolipoprotein E), 19 loci reached genome-wide significance (P < 5 × 10−8) in the combined stage 1 and stage 2 analysis, of which 11 are newly associated with Alzheimer's disease

Genome Analyses of &gt;200,000 Individuals Identify 58 Loci for Chronic Inflammation and Highlight Pathways that Link Inflammation and Complex Disorders

C-reactive protein (CRP) is a sensitive biomarker of chronic low-grade inflammation and is associated with multiple complex diseases. The genetic determinants of chronic inflammation remain largely unknown, and the causal role of CRP in several clinical outcomes is debated. We performed two genome-wide association studies (GWASs), on HapMap and 1000 Genomes imputed data, of circulating amounts of CRP by using data from 88 studies comprising 204,402 European individuals. Additionally, we performed in silico functional analyses and Mendelian randomization analyses with several clinical outcomes. The GWAS meta-analyses of CRP revealed 58 distinct genetic loci (p &lt;5 x 10(-8)). After adjustment for body mass index in the regression analysis, the associations at all except three loci remained. The lead variants at the distinct loci explained up to 7.0% of the variance in circulating amounts of CRP. We identified 66 gene sets that were organized in two substantially correlated clusters, one mainly composed of immune pathways and the other characterized by metabolic pathways in the liver. Mendelian randomization analyses revealed a causal protective effect of CRP on schizophrenia and a risk-increasing effect on bipolar disorder. Our findings provide further insights into the biology of inflammation and could lead to interventions for treating inflammation and its clinical consequences.</p