Adiabatic Control of Spin-Wave Propagation using Magnetisation Gradients

Spin waves are of large interest as data carriers for future logic devices. However, due to the strong anisotropic dispersion relation of dipolar spin-waves in in-plane magnetised films the realisation of two-dimensional information transport remains a challenge. Bending of the energy flow is prohibited since energy and momentum of spin waves cannot be conserved while changing the direction of wave propagation. Thus, non-linear or non-stationary mechanisms are usually employed. Here, we propose to use reconfigurable laser-induced magnetisation gradients to break the system's translational symmetry. The resulting changes in the magnetisation shift the dispersion relations locally and allow for operating with different spin-wave modes at the same frequency. Spin-wave momentum is first transformed via refraction at the edge of the magnetisation gradient region and then adiabatically modified inside it. Along these lines the spin-wave propagation direction can be controlled in a broad frequency range with high efficiency

Application of general semi-infinite Programming to Lapidary Cutting Problems

We consider a volume maximization problem arising in gemstone cutting industry. The problem is formulated as a general semi-infinite program (GSIP) and solved using an interiorpoint method developed by Stein. It is shown, that the convexity assumption needed for the convergence of the algorithm can be satisfied by appropriate modelling. Clustering techniques are used to reduce the number of container constraints, which is necessary to make the subproblems practically tractable. An iterative process consisting of GSIP optimization and adaptive refinement steps is then employed to obtain an optimal solution which is also feasible for the original problem. Some numerical results based on realworld data are also presented

CFD simulation of nanofiber-enhanced air filter media

The first step in a CFD analysis of filter media flow is to create a computational domain geometry which imitates the simulated media as closely as is practical. The media in the present study combined a relatively flat web of nanofibers with a cellulosic fiber support media. A CFD grid suited to calculating the flow patterns through the cellulosic media structure would be far too coarse to simulate flow around the nanofiber web elements. This scale difference forces some assumption about the interaction between the media layers. Our models are limited to two dimensions, representing cross-sections cut through the media. Our initial studies modeled the nanofiber web alone, on the assumption that the flow around the nanofibers is not greatly influenced by the presence of the downstream cellulosic fibers. Our image-analysis technique samples the distribution of fiber diameters by scribing parallel lines across the image. The diameter of the web element at each line/fiber crossing is tabulated. An estimate is made of the maximum width on the image for which the web element cross-section can be considered circular. We make the assumption that the relatively flat web elements linking round sections have oval cross-sections, all of the same thickness. We found that the distribution of web element widths is “doubly-truncated log-normal”, meaning that both lower and upper limits to the widths exist. This geometry was used with a CFD code to calculate particle capture, and compared to results of tests on the actual media