Tax Policy and CO2 Emissions – An Econometric Analysis of the German Automobile Market

In addition to efficiency standards and consumer information, car-related taxes constitute one of three pillars of the European Commission’s strategy to reduce CO2 emissions from passenger cars.A longstanding question concerns the effectiveness of such taxes in determining the car-purchasing behavior of households. Several recent studies suggest that purchases are primarily determined by retail costs rather than by taxes, the latter of which are typically incurred over the lifetime of the car. Using panel data on new-car registrations in Germany, Europe’s largest car market, the present paper addresses this issue with an econometric analysis of the impact of fuel costs and circulation taxes on car market shares. By employing a nested logit model that explicitly recognizes the segmented structure of the car market, the analysis takes account of correlation in unobserved shocks among cars belonging to the same market segment. Moreover, given the panel structure of the data, a fixed effects estimator is employed to control for the influence of unobservable, timeinvariant automobile attributes that could otherwise induce biases in the estimated coefficients. Contrasting with much of the evidence garnered to date, the results suggest that circulation taxes and fuel costs significantly determine car market shares, and hence may serve as effective instruments in influencing the composition of the car fleet and associated CO2 emissions.Fuel tax, circulation tax, car market, Germany, panel data, nested logit model

Convergence analysis of energy conserving explicit local time-stepping methods for the wave equation

Local adaptivity and mesh refinement are key to the efficient simulation of wave phenomena in heterogeneous media or complex geometry. Locally refined meshes, however, dictate a small time-step everywhere with a crippling effect on any explicit time-marching method. In [18] a leap-frog (LF) based explicit local time-stepping (LTS) method was proposed, which overcomes the severe bottleneck due to a few small elements by taking small time-steps in the locally refined region and larger steps elsewhere. Here a rigorous convergence proof is presented for the fully-discrete LTS-LF method when combined with a standard conforming finite element method (FEM) in space. Numerical results further illustrate the usefulness of the LTS-LF Galerkin FEM in the presence of corner singularities

A New Instrument for the Determination of Young’s Modulus

The apparatus used for the determination of Young\u27s modulus in the elementary laboratory at Drake has been the vertical suspended wire type, in which the sample under test is loaded and readings taken directly by means of a vernier attached to the wire. Although the readings are accurate to one one-hundredth of a centimeter, the scale cannot be conveniently read, the measurement of the length of the wire necessitates the use of a ladder, and the heavy weights are not easily handled. It is hoped that this new instrument will facilitate the experiment, although it is recognized that the weight of the wire, and friction in the bearings and gauge, may introduce slight errors

Multi-level local time-stepping methods of Runge-Kutta type forwave equations

Local mesh refinement significantly in uences the performance of explicit time-stepping methods for numerical wave propagation. Local time-stepping (LTS) methods improve the efficiency by using smaller time-steps precisely where the smallest mesh elements are located, thus permitting a larger time-step in the coarser regions of the mesh without violating the stability condition. However, when the mesh contains nested patches of refinement, any local time-step will be unnecessarily small in some regions. To allow for an appropriate time-step at each level of mesh refinement, multi-level local time-stepping (MLTS) methods have been proposed. Starting from the Runge{Kutta-based LTS methods derived by Grote et al. [17], we propose explicit MLTS methods of arbitrarily high accuracy. Numerical experiments with finite difference and continuous finite element spatial discretizations illustrate the usefulness of the novel MLTS methods and show that they retain the high accuracy and stability of the underlying Runge{Kutta methods

Imaging stray magnetic field of individual ferromagnetic nanotubes

We use a scanning nanometer-scale superconducting quantum interference device to map the stray magnetic field produced by individual ferromagnetic nanotubes (FNTs) as a function of applied magnetic field. The images are taken as each FNT is led through magnetic reversal and are compared with micromagnetic simulations, which correspond to specific magnetization configurations. In magnetic fields applied perpendicular to the FNT long axis, their magnetization appears to reverse through vortex states, i.e.\ configurations with vortex end domains or -- in the case of a sufficiently short FNT -- with a single global vortex. Geometrical imperfections in the samples and the resulting distortion of idealized mangetization configurations influence the measured stray-field patterns.Comment: 14 pages, 4 figure

Dynamic cantilever magnetometry of reversal processes and phase transitions in individual nanomagnets

Magnetic materials constitute a field of research covered by continuous and large interest. Their broad use in various areas and their potential adaption in novel and promising applications motivates the search for new materials and investigation on their fundamental properties. Magnetic samples are in fact candidates for applications in various fields. Especially their potential adaption in high density magnetic storage media increased in the recent years the interest in investigating different types and shapes of magnetic materials. Potential carriers of information could be for instance domain walls or magnetic skyrmions. A fundamental knowledge about the stability, the size and the controllability is needed before any kind of magnetic material can be implemented into a device. The motivation of this thesis is to give a contribution to the understanding of the growing, interesting and versatile field of magnetic materials by using dynamic cantilever magnetometry (DCM), which is sensitive, non-invasive and compatible to a broad range of samples with different properties. Using DCM we provide both complimentary and new information about the properties of novel or well-known magnetic materials, taking advantage of the high sensitivity of nanomechanical resonators. In fact, we demonstrate the use of DCM, in combination with numerical simulations, to study the process of magnetic reversal of short ferromagnetic (FM) nanotubes (NTs). This reversal is driven by the nucleation of vortices at the end of the tubes and shows a strong aspect-ratio dependence. For instance, short FM NTs go through a vortex state and tubes above a certain length through a mixed state composed of a vortex at each end of the tube and an axial domain in the center. Apart from the aspect ratio, we find that the shape of the ends and impurities have a significant influence on the starting of the reversal process and how it evolves. A precise knowledge of the magnetic reversal is important, since a reliable process is needed for applications like magnetic storage. We further investigate the stability of the skyrmion lattice phase of two different materials carrying the two different types of skyrmions. We measure MnSi nanowires (NWs) hosting Bloch-type skyrmions and a GaV4S8 single crystal carrying Néel skyrmions. During the studies of MnSi NWs we observe an unexpectedly stable skyrmion phase, extending from 29 K down to at least 0.4 K. The stability of the skyrmion lattice is strongly dependent on the applied magnetic field direction. An extended skyrmion lattice is present only if the long axis of the NW is parallel to the magnetic field. This stabilization occurs despite of the fact that the dimensions of the NW are too large to spatially confine the skyrmion lattice. In fact, an important difference between a NW and a single-crystal bulk sample is that a NW has an especially large surface-to-volume ratio for surfaces perpendicular to the long axis of the wire. The demagnetization influence of theses surfaces may produce an effective magnetic anisotropy which suppresses the conical phase, and therefore, in combination with a parallel applied magnetic field, stabilize and extend the skyrmion lattice. The investigation of a single-crystal of GaV4S8 also results in a surprising stability of the skyrmion lattice phase. In this case, we study the occurrence of the skyrmion phase depending on the orientation of the applied magnetic field. We find the skyrmion lattice still formed with a misalignment of 77:1˚ ± 2:3̊ between the [111] crystal axis, which is the axis along which the skyrmions form in this material, and the applied magnetic field direction. The stability of the skyrmion phase is correlated with the strength of the uniaxial anisotropy present in this material. Since the observed stability is higher than what the theoretical model predicts, for the moment we cannot conclude on the strength of the anisotropy, but the findings could help to refine the model, so that it may include all relevant interactions and fit the experimental observations

Observation of vortex-nucleated magnetization reversal in individual ferromagnetic nanotubes

The reversal of a uniform axial magnetization in a ferromagnetic nanotube (FNT) has been predicted to nucleate and propagate through vortex domains forming at the ends. In dynamic cantilever magnetometry measurements of individual FNTs, we identify the entry of these vortices as a function of applied magnetic field and show that they mark the nucleation of magnetization reversal. We find that the entry field depends sensitively on the angle between the end surface of the FNT and the applied field. Micromagnetic simulations substantiate the experimental results and highlight the importance of the ends in determining the reversal process. The control over end vortex formation enabled by our findings is promising for the production of FNTs with tailored reversal properties.Comment: 20 pages, 13 figure