Spectral deferred corrections with fast-wave slow-wave splitting

The paper investigates a variant of semi-implicit spectral deferred corrections (SISDC) in which the stiff, fast dynamics correspond to fast propagating waves ("fast-wave slow-wave problem"). We show that for a scalar test problem with two imaginary eigenvalues iλ_fast, iλ_slow, having Δt(|λ_fast|+|λ_slow|)<1 is sufficient for the fast-wave slow-wave SDC (FWSW-SDC) iteration to converge and that in the limit of infinitely fast waves the convergence rate of the non-split version is retained. Stability function and discrete dispersion relation are derived and show that the method is stable for essentially arbitrary fast-wave CFL numbers as long as the slow dynamics are resolved. The method causes little numerical diffusion and its semi-discrete phase speed is accurate also for large wave number modes. Performance is studied for an acoustic-advection problem and for the linearised Boussinesq equations, describing compressible, stratified flow. FWSW-SDC is compared to a diagonally implicit Runge-Kutta (DIRK) and IMEX Runge-Kutta (IMEX) method and found to be competitive in terms of both accuracy and cost

Identifying and assessing the implementation of human rights decisions

Assessing the extent to which states have implemented the decisions of supranational human rights bodies is a challenging task. It requires supranational bodies—be they judicial, quasi-judicial or political—to create an evidence-based public record of the status quo of implementation at any point in time and determine whether the measures taken do, in fact, satisfy the requirements of the decision. This, in turn, relies upon states engaging in good faith, victims having a voice, and civil society organisations seizing the opportunity to influence the follow-up process. Using empirical data from interviews in selected states in the African, Inter-American and European regions, and within regional and United Nations bodies, this article argues that in no human rights ‘system’ are all these expectations met, in part because follow-up work is inadequately resourced. It argues that supranational bodies should proactively seek out diverse sources of information and adopt more transparent and responsive working methods so as to enable ‘real time’ participation by all interested parties. The article concludes with recommendations for supranational bodies, and state and non-state actors

Irreversible effects of memory

The steady state of a Langevin equation with short ranged memory and coloured noise is analyzed. When the fluctuation-dissipation theorem of second kind is not satisfied, the dynamics is irreversible, i.e. detailed balance is violated. We show that the entropy production rate for this system should include the power injected by ``memory forces''. With this additional contribution, the Fluctuation Relation is fairly verified in simulations. Both dynamics with inertia and overdamped dynamics yield the same expression for this additional power. The role of ``memory forces'' within the fluctuation-dissipation relation of first kind is also discussed.Comment: 6 pages, 1 figure, publishe

Work distribution for the driven harmonic oscillator with time-dependent strength: Exact solution and slow driving

We study the work distribution of a single particle moving in a harmonic oscillator with time-dependent strength. This simple system has a non-Gaussian work distribution with exponential tails. The time evolution of the corresponding moment generating function is given by two coupled ordinary differential equations that are solved numerically. Based on this result we study the behavior of the work distribution in the limit of slow but finite driving and show that it approaches a Gaussian distribution arbitrarily well

Probability density functions of work and heat near the stochastic resonance of a colloidal particle

We study experimentally and theoretically the probability density functions of the injected and dissipated energy in a system of a colloidal particle trapped in a double well potential periodically modulated by an external perturbation. The work done by the external force and the dissipated energy are measured close to the stochastic resonance where the injected power is maximum. We show a good agreement between the probability density functions exactly computed from a Langevin dynamics and the measured ones. The probability density function of the work done on the particle satisfies the fluctuation theorem

Comparing Computing Platforms for Deep Learning on a Humanoid Robot

The goal of this study is to test two different computing platforms with respect to their suitability for running deep networks as part of a humanoid robot software system. One of the platforms is the CPU-centered Intel NUC7i7BNH and the other is a NVIDIA Jetson TX2 system that puts more emphasis on GPU processing. The experiments addressed a number of benchmarking tasks including pedestrian detection using deep neural networks. Some of the results were unexpected but demonstrate that platforms exhibit both advantages and disadvantages when taking computational performance and electrical power requirements of such a system into account.Comment: 12 pages, 5 figure

Current-Induced Spin Polarization in Gallium Nitride

Electrically generated spin polarization is probed directly in bulk GaN using Kerr rotation spectroscopy. A series of n-type GaN epilayers are grown in the wurtzite phase both by molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) with a variety of doping densities chosen to broadly modulate the transverse spin lifetime, T2*. The spin polarization is characterized as a function of electrical excitation energy over a range of temperatures. Despite weak spin-orbit interactions in GaN, a current-induced spin polarization (CISP) is observed in the material at temperatures of up to 200 K.Comment: 16 pages, 3 figure

Mobility and Diffusion of a Tagged Particle in a Driven Colloidal Suspension

We study numerically the influence of density and strain rate on the diffusion and mobility of a single tagged particle in a sheared colloidal suspension. We determine independently the time-dependent velocity autocorrelation functions and, through a novel method, the response functions with respect to a small force. While both the diffusion coefficient and the mobility depend on the strain rate the latter exhibits a rather weak dependency. Somewhat surprisingly, we find that the initial decay of response and correlation functions coincide, allowing for an interpretation in terms of an 'effective temperature'. Such a phenomenological effective temperature recovers the Einstein relation in nonequilibrium. We show that our data is well described by two expansions to lowest order in the strain rate.Comment: submitted to EP

Effective Confinement as Origin of the Equivalence of Kinetic Temperature and Fluctuation-Dissipation Ratio in a Dense Shear Driven Suspension

We study response and velocity autocorrelation functions for a tagged particle in a shear driven suspension governed by underdamped stochastic dynamics. We follow the idea of an effective confinement in dense suspensions and exploit a time-scale separation between particle reorganization and vibrational motion. This allows us to approximately derive the fluctuation-dissipation theorem in a "hybrid" form involving the kinetic temperature as an effective temperature and an additive correction term. We show numerically that even in a moderately dense suspension the latter is negligible. We discuss similarities and differences with a simple toy model, a single trapped particle in shear flow

Effective free energy for pinned membranes

We consider membranes adhered through specific receptor-ligand bonds. Thermal undulations of the membrane induce effective interactions between adhesion sites. We derive an upper bound to the free energy that is independent of interaction details. To lowest order in a systematic expansion we obtain two-body interactions which allow to map the free energy onto a lattice gas with constant density. The induced interactions alone are not strong enough to lead to a condensation of individual adhesion sites. A measure of the thermal roughness is shown to depend on the inverse square root of the density of adhesion sites, which is in good agreement with previous computer simulations.Comment: to appear as a Rapid Communication in Phys. Rev.