Rotational hysteresis of the exchange anisotropy direction in Co/FeMn thin films

We have investigated the effects of rotating an applied field on the exchange anisotropy in Co/FeMn thin films. When the applied field is initially along the cooling field direction, the longitudinal hysteresis loop has a maximum coercivity and the transverse hysteresis loop is flat, indicating that the exchange field is along the cooling field direction. When the applied field angle is rotated away and then restored to the original field cooling direction, the exchange anisotropy direction has changed. The rotation of the exchange field direction trails the applied field and is hysteretic. The rotational hysteresis of the exchange field direction is due to the weak anisotropy in thin FeMn layers, and decreases with increasing FeMn thickness.Comment: 13 pages, 3 figures, to appear in J. Appl. Phy

Solving the Direction Field for Discrete Agent Motion

Models for pedestrian dynamics are often based on microscopic approaches allowing for individual agent navigation. To reach a given destination, the agent has to consider environmental obstacles. We propose a direction field calculated on a regular grid with a Moore neighborhood, where obstacles are represented by occupied cells. Our developed algorithm exactly reproduces the shortest path with regard to the Euclidean metric.Comment: 8 pages, 4 figure

Magnetic waves in a stratified medium: dispersion relations and exact solutions

We solve for waves in an isothermal, stratified medium with a magnetic field that points along a direction perpendicular to that of gravity and varies exponentially in the direction of gravity. For waves propagating along the magnetic field, we calculate approximate dispersion relation as a function of the magnetic field strength. We also find exact solutions for two different cases: (a) waves propagating along the direction of the magnetic field and (b) waves propagating along the direction of gravity. In each of these cases, we find solutions in terms of either confluent hypergeometric functions or Gauss hypergeometric functions depending on whether the ratio of the scale height of the magnetic field over the density scale height is equal to two or not.Comment: 9 pages, 4 figures, Submitte

Direction-Dependent Polarised Primary Beams in Wide-Field Synthesis Imaging

The process of wide-field synthesis imaging is explored, with the aim of understanding the implications of variable, polarised primary beams for forthcoming Epoch of Reionisation experiments. These experiments seek to detect weak signatures from redshifted 21cm emission in deep residual datasets, after suppression and subtraction of foreground emission. Many subtraction algorithms benefit from low side-lobes and polarisation leakage at the outset, and both of these are intimately linked to how the polarised primary beams are handled. Building on previous contributions from a number of authors, in which direction-dependent corrections are incorporated into visibility gridding kernels, we consider the special characteristics of arrays of fixed dipole antennas operating around 100-200 MHz, looking towards instruments such as the Square Kilometre Array (SKA) and the Hydrogen Epoch of Reionization Arrays (HERA). We show that integrating snapshots in the image domain can help to produce compact gridding kernels, and also reduce the need to make complicated polarised leakage corrections during gridding. We also investigate an alternative form for the gridding kernel that can suppress variations in the direction-dependent weighting of gridded visibilities by 10s of dB, while maintaining compact support.Comment: 15 pages, 4 figures. Accepted for publication in JA