Technical Efficiency of Automobiles – A Nonparametric Approach Incorporating Carbon Dioxide Emissions

We conduct an empirical analysis of the technical efficiency of cars sold in Germany in 2010. The analysis is performed using traditional data envelopment analysis (DEA) as well as directional distance functions (DDF). The approach of DDF allows incorporating the reduction of carbon dioxide emissions as an environmental goal in the efficiency analysis. A frontier separation approach is used to gain deeper insight for different car classes and regions of origin. Natural gas driven cars and sports-utility-vehicles are also treated as different groups. The results show that the efficiency measurement is significantly influenced by the incorporation of carbon dioxide emissions. Moreover, we find that there is indeed a trade-off between technological performance and environmental performance.nonparametric efficiency measurement, directional distance function, automobiles, air pollution

Accurate calculation of the transverse anisotropy in perpendicularly magnetized multilayers

The transverse anisotropy constant and the related D\"oring mass density are key parameters of the one-dimensional model to describe the motion of magnetic domain walls. So far, no general framework is available to determine these quantities from static characterizations such as magnetometry measurements. Here, we derive a universal analytical expression to calculate the transverse anisotropy constant for the important class of perpendicular magnetic multilayers. All the required input parameters of the model, such as the number of repeats, the thickness of a single magnetic layer, and the layer periodicity, as well as the effective perpendicular anisotropy, the saturation magnetization, and the static domain wall width are accessible by static sample characterizations. We apply our model to a widely used multilayer system and find that the effective transverse anisotropy constant is a factor 7 different from the when using the conventional approximations, showing the importance of using our analysis scheme

Optimal Directions for Directional Distance Functions: An Exploration of Potential Reductions of Greenhouse Gases

This study explores the reduction potential of greenhouse gases for major pollution emitting countries of the world using nonparametric productivity measurement methods and directional distance functions. In contrast to the existing literature we apply optimization methods to endogenously determine optimal directions for the efficiency analysis. These directions represent the compromise of output enhancement and emissions reduction. The results show that for reasonable directions the adoption of best-practices would lead to sizable emission reductions in a range of about 20 percent compared to current levels

Multiscale Model Approach for Magnetization Dynamics Simulations

Simulations of magnetization dynamics in a multiscale environment enable rapid evaluation of the Landau-Lifshitz-Gilbert equation in a mesoscopic sample with nanoscopic accuracy in areas where such accuracy is required. We have developed a multiscale magnetization dynamics simulation approach that can be applied to large systems with spin structures that vary locally on small length scales. To implement this, the conventional micromagnetic simulation framework has been expanded to include a multiscale solving routine. The software selectively simulates different regions of a ferromagnetic sample according to the spin structures located within in order to employ a suitable discretization and use either a micromagnetic or an atomistic model. To demonstrate the validity of the multiscale approach, we simulate the spin wave transmission across the regions simulated with the two different models and different discretizations. We find that the interface between the regions is fully transparent for spin waves with frequency lower than a certain threshold set by the coarse scale micromagnetic model with no noticeable attenuation due to the interface between the models. As a comparison to exact analytical theory, we show that in a system with Dzyaloshinskii-Moriya interaction leading to spin spiral, the simulated multiscale result is in good quantitative agreement with the analytical calculation

Technical Efficiency of Automobiles – A Nonparametric Approach Incorporating Carbon Dioxide Emissions

We conduct an empirical analysis of the technical efficiency of cars sold in Germany in 2010. The analysis is performed using traditional data envelopment analysis (DEA) as well as directional distance functions (DDF). The approach of DDF allows incorporating the reduction of carbon dioxide emissions as an environmental goal in the efficiency analysis. A frontier separation approach is used to gain deeper insight for different car classes and regions of origin. Natural gas driven cars and sports-utility-vehicles are also treated as different groups. The results show that the efficiency measurement is significantly influenced by the incorporation of carbon dioxide emissions. Moreover, we find that there is indeed a trade-off between technological performance and environmental performance

Multiscale simulations of topological transformations in magnetic Skyrmions

Magnetic Skyrmions belong to the most interesting spin structures for the development of future information technology as they have been predicted to be topologically protected. To quantify their stability, we use an innovative multiscale approach to simulating spin dynamics based on the Landau-Lifshitz-Gilbert equation. The multiscale approach overcomes the micromagnetic limitations that have hindered realistic studies using conventional techniques. We first demonstrate how the stability of a Skyrmion is influenced by the refinement of the computational mesh and reveal that conventionally employed traditional micromagnetic simulations are inadequate for this task. Furthermore, we determine the stability quantitatively using our multiscale approach. As a key operation for devices, the process of annihilating a Skyrmion by exciting it with a spin polarized current pulse is analyzed, showing that Skyrmions can be reliably deleted by designing the pulse shape

Inertia and chiral edge modes of a skyrmion magnetic bubble

The dynamics of a vortex in a thin-film ferromagnet resembles the motion of a charged massless particle in a uniform magnetic field. Similar dynamics is expected for other magnetic textures with a nonzero skyrmion number. However, recent numerical simulations revealed that skyrmion magnetic bubbles show significant deviations from this model. We show that a skyrmion bubble possesses inertia and derive its mass from the standard theory of a thin-film ferromagnet. Besides center-of-mass motion, other low energy modes are waves on the edge of the bubble traveling with different speeds in opposite directions.Comment: updated simulation detail