Showing papers by "Jürg Fröhlich published in 2014"

EMF monitoring-concepts, activities, gaps and options.

Abstract: Exposure to electromagnetic fields (EMF) is a cause of concern for many people. The topic will likely remain for the foreseeable future on the scientific and political agenda, since emissions continue to change in characteristics and levels due to new infrastructure deployments, smart environments and novel wireless devices. Until now, systematic and coordinated efforts to monitor EMF exposure are rare. Furthermore, virtually nothing is known about personal exposure levels. This lack of knowledge is detrimental for any evidence-based risk, exposure and health policy, management and communication. The main objective of the paper is to review the current state of EMF exposure monitoring activities in Europe, to comment on the scientific challenges and deficiencies, and to describe appropriate strategies and tools for EMF exposure assessment and monitoring to be used to support epidemiological health research and to help policy makers, administrators, industry and consumer representatives to base their decisions and communication activities on facts and data.

Effective Dynamics of a Tracer Particle Interacting with an Ideal Bose Gas

Abstract: We study a system consisting of a heavy quantum particle, called the tracer particle, coupled to an ideal gas of light Bose particles, the ratio of masses of the tracer particle and a gas particle being proportional to the gas density. All particles have non-relativistic kinematics. The tracer particle is driven by an external potential and couples to the gas particles through a pair potential. We compare the quantum dynamics of this system to an effective dynamics given by a Newtonian equation of motion for the tracer particle coupled to a classical wave equation for the Bose gas. We quantify the closeness of these two dynamics as the mean-field limit is approached (gas density \({\to \infty}\)). Our estimates allow us to interchange the thermodynamic with the mean-field limit.

Quantum diffusion with drift and the Einstein relation. I

Abstract: We study the dynamics of a quantum particle hopping on a simple cubic lattice and driven by a constant external force. It is coupled to an array of identical, independent thermal reservoirs consisting of free, massless Bose fields, one at each site of the lattice. When the particle visits a site x of the lattice it can emit or absorb field quanta of the reservoir at x. Under the assumption that the coupling between the particle and the reservoirs and the driving force are sufficiently small, we establish the following results: The ergodic average over time of the state of the particle approaches a non-equilibrium steady state describing a non-zero mean drift of the particle. Its motion around the mean drift is diffusive, and the diffusion constant and the drift velocity are related to one another by the Einstein relation.

Dynamics of Sound Waves in an Interacting Bose Gas

Abstract: We consider a non-relativistic quantum gas of $N$ bosonic atoms confined to a box of volume $\Lambda$ in physical space. The atoms interact with each other through a pair potential whose strength is inversely proportional to the density, $\rho=\frac{N}{\Lambda}$, of the gas. We study the time evolution of coherent excitations above the ground state of the gas in a regime of large volume $\Lambda$ and small ratio $\frac{\Lambda}{\rho}$. The initial state of the gas is assumed to be close to a \textit{product state} of one-particle wave functions that are approximately constant throughout the box. The initial one-particle wave function of an excitation is assumed to have a compact support independent of $\Lambda$. We derive an effective non-linear equation for the time evolution of the one-particle wave function of an excitation and establish an explicit error bound tracking the accuracy of the effective non-linear dynamics in terms of the ratio $\frac{\Lambda}{\rho}$. We conclude with a discussion of the dispersion law of low-energy excitations, recovering Bogolyubov's well-known formula for the speed of sound in the gas, and a dynamical instability for attractive two-body potentials.

Messsystem und -verfahren zur messung von parametern in einem körpergewebe

Abstract: Ein Messsystem und -verfahren zur Messung wenigstens eines Parameters in einem Korpergewebe umfasst wenigstens eine Messvorrichtung zum Anbringen am Korper, eine optische Einheit zur Emission von Lichtwellen, wobei wenigstens eine Wellenlange der Lichtwellen im Bereich der Absorption eines Korperparameters liegt, wenigstens einen Lichtleiter zwischen optischer Einheit und Messvorrichtung zur Ubermittlung von Lichtwellen und eine Auswerteeinheit zur Auswertung von Messwellen. Von der optischen Einheit emittierte Lichtwellen sind mittels der Messvorrichtung in ein optisches Messvolumen im Korpergewebe einstrahlbar und aus dem Me ssvolumen von der Messvorrichtung empfangene Messwellen sind aus dem Korpergewebe an die Auswerteeinheit ubermittelbar. Die Auswerteeinheit umfasst einen Transformationsalgorithmus, der eine Pulsatilitat eines im Messvolumen gemessenen Korperparameters in einen Parameter des Drucks in dem Korpergewebe transformiert, wobei der Korperparameter aus der Bestimmung der Absorption der Lichtwellen ermittelt ist.

Quantum Electrodynamics of Atomic Resonances

Abstract: A simple model of an atom interacting with the quantized electromagnetic field is studied. The atom has a finite mass $m$, finitely many excited states and an electric dipole moment, $\vec{d}_0 = -\lambda_{0} \vec{d}$, where $\| d^{i}\| = 1,$ $ i=1,2,3,$ and $\lambda_0$ is proportional to the elementary electric charge. The interaction of the atom with the radiation field is described with the help of the Ritz Hamiltonian, $-\vec{d}_0\cdot \vec{E}$, where $\vec{E}$ is the electric field, cut off at large frequencies. A mathematical study of the Lamb shift, the decay channels and the life times of the excited states of the atom is presented. It is rigorously proven that these quantities are analytic functions of the momentum $\vec{p}$ of the atom and of the coupling constant $\lambda_0$, provided $|\vec{p}| < mc$ and $| \Im\vec{p} |$ and $| \lambda_{0} |$ are sufficiently small. The proof relies on a somewhat novel inductive construction involving a sequence of `smooth Feshbach-Schur maps' applied to a complex dilatation of the original Hamiltonian, which yields an algorithm for the calculation of resonance energies that converges super-exponentially fast.