Numerical integrators for motion under a strong constraining force

This paper deals with the numerical integration of Hamiltonian systems in which a stiff anharmonic potential causes highly oscillatory solution behavior with solution-dependent frequencies. The impulse method, which uses micro- and macro-steps for the integration of fast and slow parts, respectively, does not work satisfactorily on such problems. Here it is shown that variants of the impulse method with suitable projection preserve the actions as adiabatic invariants and yield accurate approximations, with macro-stepsizes that are not restricted by the stiffness parameter

A Compressed Sampling and Dictionary Learning Framework for WDM-Based Distributed Fiber Sensing

We propose a compressed sampling and dictionary learning framework for fiber-optic sensing using wavelength-tunable lasers. A redundant dictionary is generated from a model for the reflected sensor signal. Imperfect prior knowledge is considered in terms of uncertain local and global parameters. To estimate a sparse representation and the dictionary parameters, we present an alternating minimization algorithm that is equipped with a pre-processing routine to handle dictionary coherence. The support of the obtained sparse signal indicates the reflection delays, which can be used to measure impairments along the sensing fiber. The performance is evaluated by simulations and experimental data for a fiber sensor system with common core architecture.Comment: Accepted for publication in Journal of the Optical Society of America A [ \copyright\ 2017 Optical Society of America.]. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibite

Return Migration: Theory and Empirical Evidence

In this paper we discuss forms of migration that are non-permanent. We focus on temporary migrations where the decision to return is taken by the immigrant. These migrations are likely to be frequent, and we provide some evidence for the UK. We then develop a simple model which rationalizes the decision of a migrant to return to his home country, despite a persistently higher wage in the host country. We consider three motives for a temporary migration: Differences in relative prices in host- and home country, complementarities between consumption and the location where consumption takes place, and the possibility of accumulating human capital abroad which enhances the immigrant's earnings potential back home. For the last return motive, we discuss extensions which allow for immigrant heterogeneity, and develop implications for selective in- and out- migration.Life Cycle Models, International Migration, Return Migration

DIS on a polarized spin-1 target with spectator tagging

We discuss the process of deep-inelastic electron scattering (DIS) on the polarized deuteron with detection of a nucleon in the nuclear fragmentation region (“spectator tagging”). We cover (a) the general structure of the semi-inclusive DIS cross section on a spin-1 target; (b) the tagged structure functions in the impulse approximation, where deuteron structure is described by the NN light-front wave function; (c) the extraction of free neutron structure through on-shell ex-trapolation in the recoil proton momentum. As an application we consider the extraction of the neutron structure function F 2n and spin structure function g 1n through electron scattering on the (un)polarized deuteron with proton tagging and on-shell extrapolation. Such measurements would be possible at an Electron-Ion Collider (EIC) with polarized deuteron beams and forward proton detectors

Return Migration, Human Capital Accumulation and the Brain Drain

In this paper we present a model that explains migrations as decisions that respond to where human capital can be acquired more efficiently, and where the return to human capital is highest. The basic framework is a dynamic Roy model in which a worker possesses two distinct skills that can be augmented by learning by doing. There are different implicit prices, in different countries and different rates of skill accumulation. Our analysis contributes to the literature on the selection of immigrants and return migrants by offering a richer framework that may help to accommodate selection of emigrants and return migrants that are not immediately compatible with the one-dimensional skill model. Our analysis also has implications for the debate on brain drain and brain gain. In the two skills model presented here, return migration can lead to a mitigation of the brain drain, or even the creation of a "brain gain", where those who return bring the home country augmented local skills.Return migration, human capital accumulation, comparative advantage, brain drain

Temperature- and Field Dependent Characterization of a Twisted Stacked-Tape Cable

The Twisted Stacked-Tape Cable (TSTC) is one of the major high temperature superconductor cable concepts combining scalability, ease of fabrication and high current density making it a possible candidate as conductor for large scale magnets. To simulate the boundary conditions of such a magnets as well as the temperature dependence of Twisted Stacked-Tape Cables a 1.16 m long sample consisting of 40, 4 mm wide SuperPower REBCO tapes is characterized using the "FBI" (force - field - current) superconductor test facility of the Institute for Technical Physics (ITEP) of the Karlsruhe Institute of Technology (KIT). In a first step, the magnetic background field is cycled while measuring the current carrying capabilities to determine the impact of Lorentz forces on the TSTC sample performance. In the first field cycle, the critical current of the TSTC sample is tested up to 12 T. A significant Lorentz force of up to 65.6 kN/m at the maximal magnetic background field of 12 T result in a 11.8 % irreversible degradation of the current carrying capabilities. The degradation saturates (critical cable current of 5.46 kA at 4.2 K and 12 T background field) and does not increase in following field cycles. In a second step, the sample is characterized at different background fields (4-12 T) and surface temperatures (4.2-37.8 K) utilizing the variable temperature insert of the "FBI" test facility. In a third step, the performance along the length of the sample is determined at 77 K, self-field. A 15 % degradation is obtained for the central part of the sample which was within the high field region of the magnet during the in-field measurements