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In a thin magnetic nanostripe, an antivortex nucleates inside a moving domain wall when driven by an in-plane magnetic field greater than the so-called Walker field. The nucleated antivortex must cross the width of the nanostripe before the domain wall can propagate again, leading to low average domain wall speeds. A large out-of-plane magnetic field, applied perpendicularly to the plane of the nanostripe, inhibits the nucleation of the antivortex leading to fast domain wall speeds for all in-plane driving fields. We present micromagnetic simulation results relating the antivortex dynamics to the strength of the out-of-plane field. An asymmetry in the motion is observed which depends on the alignment of the antivortex core magnetic moments to the direction of the out-of-plane field. The size of the core is directly related to its crossing speed, both depending on the strength of the perpendicular field and the alignment of the core moments and direction of the out-of-plane field. [ABSTRACT FROM AUTHOR]

We present results on the image distortion or ‘‘modulation’’ produced when a wedge and strip anode (WSA) position readout is used with a charge cloud of size comparable with that of the pattern repeat pitch. We use a standard detector consisting of a microchannel plate (MCP) intensifier and wedge and strip anode to investigate the effect of detector operating parameters on image modulation. We find that modulation depends on the MCP gain of each event and on the MCP voltage, and is minimized when the plates are run at high gains and with high rear MCP operating voltages. We compare the experimental results obtained using this detector with the response calculated numerically in a computer simulation. From the simulation it becomes apparent that for a detailed understanding of wedge and strip performance the microchannel plate charge cloud distribution must be considered. However, some of the general features of the wedge and strip anode performance are independent of the charge cloud form. The most important of these is that modulation distortion displaces a vertical line (parallel to the direction of increasing wedge) to another vertical line, while a horizontal line (parallel to the direction of increasing strip) is distorted into a wave-shaped curve with the periodicity of the pattern pitch. [ABSTRACT FROM AUTHOR]

We describe the fabrication and testing of antenna-coupled superconducting transition-edge bolometers for use at millimeter wavelengths. The design uses a double-slot dipole antenna connected to superconducting niobium microstrip. Band defining filters are implemented in the microstrip, which is then terminated with a load resistor. The power dissipated in the load resistor is measured by a superconducting transition-edge sensor (TES). The load resistor and TES are thermally well connected and are supported by a silicon nitride substrate. The substrate is suspended by four narrow silicon nitride legs for thermal isolation. The bolometers have been optically characterized and the spectral response is presented. This detector is a prototype element for use in an array designed for studies of the cosmic microwave background polarization. [ABSTRACT FROM AUTHOR]