The Degeneration of the Human Mind: An Analysis of Alzheimer’s Disease, A Kuhnian Perspective

In 1906, a German physician, Dr. Alois Alzheimer, specifically identified a collection of brain cell abnormalities (and the formation of plaque in the brain) as a disease, which forever changed the way scientists view degenerative cognitive disorders. Today, this brain disease bears his name, and is one of the most common diseases among the aging population. The discovery of Alzheimer’s Disease (AD) can be seen as a revolutionary, paradigmatic shift in regards to scientific discovery from a Kuhnian perspective. In that vein, the discovery presents philosophical implications for the notion of personhood and how those suffering from AD are treated in society

Nonequilibrium dynamics and magnetoviscosity of moderately concentrated magnetic liquids: A dynamic mean--field study

A mean-field Fokker-Planck equation approach to the dynamics of ferrofluids in the presence of a magnetic field and velocity gradients is proposed that incorporates magnetic dipole-dipole interactions of the colloidal particles. The model allows to study the combined effect of a magnetic field and dipolar interactions on the viscosity of the ferrofluid. It is found that dipolar interactions lead to additional non-Newtonian contributions to the stress tensor, which modify the behavior of the non-interacting system. The predictions of the present model are in qualitative agreement with experimental results, such as presence of normal stress differences, enhancement and different anisotropy of magnetoviscous effect and the dependence of the viscosity on the hydrodynamic volume fraction. A quantitative comparison of the concentration dependence of the magnetoviscosity shows good agreement with experimental results for low concentrations.Comment: 12 pages, 5 figure

Driven activation versus thermal activation

Activated dynamics in a glassy system undergoing steady shear deformation is studied by numerical simulations. Our results show that the external driving force has a strong influence on the barrier crossing rate, even though the reaction coordinate is only weakly coupled to the nonequilibrium system. This "driven activation" can be quantified by introducing in the Arrhenius expression an effective temperature, which is close to the one determined from the fluctuation-dissipation relation. This conclusion is supported by analytical results for a simplified model system.Comment: 5 pages, 3 figure

Entanglement dynamics at flat surfaces: investigations using multi-chain molecular dynamics and a single-chain slip-spring model

The dynamics of an entangled polymer melt confined in a channel by parallel plates is investigated by Molecular Dynamics (MD) simulations of a detailed, multi-chain model. A Primitive Path Analysis predicts that the density of entanglements remains approximately constant throughout the gap and drops to lower values only in the immediate vicinity of the surface. Based on these observations, we propose a coarse-grained, single-chain slip-spring model with a uniform density of slip-spring anchors and slip-links. The slip-spring model is compared to the Kremer-Grest MD bead-spring model via equilibrium correlation functions of chain orientations. Reasonably good agreement between the single-chain model and the detailed multi-chain model is obtained for chain relaxation dynamics, both away from the surface and for chains whose center of mass positions are at a distance from the surface that is less than the bulk chain radius of gyration, without introducing any additional model parameters. Our results suggest that there is no considerable drop in topological interactions for chains in the vicinity of a single flat surface. We infer from the slip-spring model that the experimental plateau modulus of a confined polymer melt may be different to a corresponding unconfined system even if there is no drop in topological interactions for the confined case

Model-free bounds on bilateral counterparty valuation

In the last years, counterparty default risk has experienced an increased interest both by academics as well as practitioners. This was especially motivated by the market turbulences and the financial crises over the past years which have highlighted the importance of counterparty default risk for uncollateralized derivatives. The following paper focuses on the pricing of derivatives subject to such counterparty risk. After a succinct introduction to the topic, a brief review of state-of-the-art methods for the calculation of bilateral counterparty value adjustments is presented. Due to some weaknesses of these models, a novel method for the determination of model-free tight lower and upper bounds on these adjustments is presented. It will be shown in detail how these bounds can be easily and eciently calculated by the solution of a corresponding linear optimization problem. It will be illustrated how usual discretization methods like Monte Carlo methods allow to reduce the calculation of bounds to an ordinary finite dimensional transportation problem, whereas a continuous time approach will lead to a general mass transportation problem. The paper is closed with several applications of these model-free bounds, like stress-testing and estimation of model reserves.Counterparty risk, CVA, model risk

Importance of depletion interactions for structure and dynamics of ferrofluids

Abstract.: The influence of attractive depletion forces on the structure and dynamics of ferrofluids is studied by computer simulations. In the presence of a magnetic field, we find that sufficiently strong depletion forces lead to an assembly of particle chains into columnar structures with hexagonal ordering inside the columns. In a planar shear flow, this ordering is destroyed, leading to strong shear thinning behavior. A pronounced anisotropy of the shear viscosity is observed. The viscosity is found to be largest when the magnetic field is oriented in the gradient direction of the flo