Operation and failure of a hairpin nucleate generator on a bubble memory chip

The dynamic operation as well as the failure modes of a hairpin nucleate bubble generator operating at 125 kHz has been studied using a high-speed optical sampling system. The hairpin generator loop consists of a 6.8-μm wide 4.2-μm gap conductor located under a 20-μm period 110° chevron propagation pattern. In stable operation in the center of the operating range, bubbles are nucleated along the hairpin conductor preserving a U shape that reflects the shape of the hairpin conductor. After nucleation, the gap of the conductor fills with a long wide domain. This long domain then shrinks to a stable position under the propagation elements with a wall velocity of 40 m/s. All velocities observed are consistent with velocities observed on free bubbles using radial expansion, except for the growth in length after nucleation during the generate pulse, where the domain grows about three times faster than would be expected. This difference is attributed to the in-plane component of the generate current field that is very nonuniform through the thickness of the sample. The failure mode for a low or short generate pulse is multibubble generation caused by nonuniform nucleation along the length of the conductors of the hairpin loop. For certain pulse characteristics at this low end of the operating range, a stable U-shaped domain is nucleated only to be cut into two domains at the end of the generate pulse as the drive field reverses the poles on the nearest chevron stack from what it was during the pulse. The failure mode at the upper end of the operating range also results in excess bubbles. Here the mechanism can be identified as the development of a wavy wall as it moves rapidly under the conductor element in the presence of a large in-plane field caused by the generate current. This distortion then increases as the domain shrinks, resulting in nobs that are pinched off to create excess bubbles. The distortion is similar to that seen during the collapse of highly expanded stripes. This failure can be cured by increasing the fall time of the generate pulse to a least 100 ns

High-frequency propagation and failure of asymmetric half-disk field access magnetic bubble device elements

High-frequency propagation characteristics and failure modes in 14-μm period, 1.8-μm gap, asymmetric half-disk field-access device were studied using a high-speed optical sampling technique. Propagation elements as well as normal and hand gun corners and chevron structures were included. The operating bias margin at 1MHz, for a structure that had 1.2 MHz as highest possible frequency, was about half of the margin for frequencies of 200 kHz and below. The phase lag between the bubble leading wall and the instantaneous rotating field direction was nearly 90° as the bubble moved through the center of the element where the lag was the greatest. The peak velocity of the leading wall of 55 m/s and the trailing wall of 46 m/s is attributed to bubble interaction with the Permalloy structure creating a ∼125 Oe in-plane field that greatly increases the free bubble "saturation" velocity

Micromagnetic characteristics of transverse diffuse domain boundaries in permalloy thin films

Transverse domain boundaries propagating in the longitudinal direction at speeds one to three orders of magnitude faster than normal domain walls are responsible for most of the lower speed reversals in magnetic thin films. Using a 10-ns exposure time Kerr magnetooptic camera, these boundaries have been photographed for a variety of applied fields in several films with thicknesses ranging from 500 to 3500 Å. High-magnification photographs of the boundary transition region reveal that the boundaries consist of small isolated areas of reversed and partially reversed magnetization in a nonreversed background. Propagation occurs by the nucleation of additional small areas of reverse magnetization within and ahead of the transition region. In a given film the width of the transition region increases as the applied field is increased. By approximating the divergence of the magnetization at the boundary as a line charge, a model has been derived which predicts the boundary widthWto beW = \frac{8M_{s}t}{H_{n}}\frac{1}{(1-H/H_{n})}where Msis the saturation magnetization andHis the applied field. The nucleation threshold Hnis the threshold at which nucleation is observed over all the film. The experimental data fit this predicted dependence quite well. The rapid increase in width of the transition region with applied field is correlated with a rapid nonlinear increase in the velocity of propagation

Dynamic behavior of domain walls in double layer self-biasing bubble garnet films

Radial expansion of bubbles and gradient bubble propagation experiments were conducted in a double layer garnet film with perpendicular anisotropy in both layers. Implanted and as-grown samples are compared. In radial expansion the side walls of the bubble exhibit a linear mobility much lower than calculated from γΔ/α. Saturation occurs at high drives (35 Oe). At drives above 50 Oe the saturation velocity of 27 m/s occurs only in the first 120 ns of the motion. After that the velocity drops to 17.5 m/s still independent of drive. This break in velocity does not occur in implanted samples, where the saturation velocity depends on implantation conditions. In gradient propagation saturation occurs at fields an order of magnitude smaller. The saturation velocity is independent of implantation, but overshoot depends strongly on it. No creep was detected. The 180° head-on domain wall between the two layers is found to have little effect on the dynamics of the side walls of the bubble. The motion of the head-on wall is also investigated and its velocity estimated. This head-on wall exhibits a linear mobility and a saturation velocity at high drives

Wall structure changes in low-loss magnetic bubble materials

Transitions between underdamped and overdamped radial motion in magnetic bubble domains are investigated in a low-loss rare-earth garnet material. Three distinct types of domain wall structures, which are present during underdamped motion, have been identified. Bubble walls were subjected to a bias field pulse (H) and tested for underdamped motion sometime (τ) later. The first type of structure follows the form H = H' exp (τ\τ_0), with 170 nsec < τ_0 < 270 nsec for the first transition, and is not statically stable. Transitions associated with the second type are characterized by a constant critical angle Ψ_c between the magnetization in the middle of the wall, and the plane of the wall. For the first transition, Ψ_c = 230°, and for the second, Ψ_c = 370°. These structures are statically stable. The third type of structure is not statically stable, and H is independent of τ. The first and second wall structure types are associated with multiple transitions while the third only exhibits a single transition

Link Coupling for Nuclear Magnetic Resonance

In an attempt to use proton magnetic resonance for regulation of magnetic fields of 10 kilogauss or more, it has been found that the conventional probe sample holder used by other investigators (1) gave inadequate, if any, resonance lines above 40 mc/sec. In such arrangements, the oscillator tank coil is at the end of a coaxial probe. The weaker lines at higher frequencies are attributed to the fact that the distributed inductance of the coaxial line becomes important as frequency is increased. To overcome this difficulty, we have employed a link-type coupling arrangement

Colloquium on Solid State Devices

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Insights in 17β-HSD1 Enzyme Kinetics and Ligand Binding by Dynamic Motion Investigation

BACKGROUND: Bisubstrate enzymes, such as 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1), exist in solution as an ensemble of conformations. 17beta-HSD1 catalyzes the last step of the biosynthesis of estradiol and, thus, it is a potentially attractive target for breast cancer treatment. METHODOLOGY/PRINCIPAL FINDINGS: To elucidate the conformational transitions of its catalytic cycle, a structural analysis of all available crystal structures was performed and representative conformations were assigned to each step of the putative kinetic mechanism. To cover most of the conformational space, all-atom molecular dynamic simulations were performed using the four crystallographic structures best describing apoform, opened, occluded and closed state of 17beta-HSD1 as starting structures. With three of them, binary and ternary complexes were built with NADPH and NADPH-estrone, respectively, while two were investigated as apoform. Free energy calculations were performed in order to judge more accurately which of the MD complexes describes a specific kinetic step. CONCLUSIONS/SIGNIFICANCE: Remarkably, the analysis of the eight long range trajectories resulting from this multi-trajectory/-complex approach revealed an essential role played by the backbone and side chain motions, especially of the betaF alphaG'-loop, in cofactor and substrate binding. Thus, a selected-fit mechanism is suggested for 17beta-HSD1, where ligand-binding induced concerted motions of the FG-segment and the C-terminal part guide the enzyme along its preferred catalytic pathway. Overall, we could assign different enzyme conformations to the five steps of the random bi-bi kinetic cycle of 17beta-HSD1 and we could postulate a preferred pathway for it. This study lays the basis for more-targeted biochemical studies on 17beta-HSD1, as well as for the design of specific inhibitors of this enzyme. Moreover, it provides a useful guideline for other enzymes, also characterized by a rigid core and a flexible region directing their catalysis

Improving implementation of evidence-based practice in mental health service delivery: protocol for a cluster randomised quasi-experimental investigation of staff-focused values interventions

BACKGROUND: There is growing acceptance that optimal service provision for individuals with severe and recurrent mental illness requires a complementary focus on medical recovery (i.e., symptom management and general functioning) and personal recovery (i.e., having a ‘life worth living’). Despite significant research attention and policy-level support, the translation of this vision of healthcare into changed workplace practice continues to elude. Over the past decade, evidence-based training interventions that seek to enhance the knowledge, attitudes, and skills of staff working in the mental health field have been implemented as a primary redress strategy. However, a large body of multi-disciplinary research indicates disappointing rates of training transfer. There is an absence of empirical research that investigates the importance of worker-motivation in the uptake of desired workplace change initiatives. ‘Autonomy’ is acknowledged as important to human effectiveness and as a correlate of workplace variables like productivity, and wellbeing. To our knowledge, there have been no studies that investigate purposeful and structured use of values-based interventions to facilitate increased autonomy as a means of promoting enhanced implementation of workplace change. METHODS: This study involves 200 mental health workers across 22 worksites within five community-managed organisations in three Australian states. It involves cluster-randomisation of participants within organisation, by work site, to the experimental (values) condition, or the control (implementation). Both conditions receive two days of training focusing on an evidence-based framework of mental health service delivery. The experimental group receives a third day of values-focused intervention and 12 months of values-focused coaching. Well-validated self-report measures are used to explore variables related to values concordance, autonomy, and self-reported implementation success. Audits of work files and staff work samples are reviewed for each condition to determine the impact of implementation. Self-determination theory and theories of organisational change are used to interpret the data. DISCUSSION: The research adds to the current knowledge base related to worker motivation and uptake of workplace practice. It describes a structured protocol that aims to enhance worker autonomy for imposed workplace practices. The research will inform how best to measure and conceptualise transfer. These findings will apply particularly to contexts where individuals are not ‘volunteers’ in requisite change processes. TRIAL REGISTRATION: ACTRN: ACTRN12613000353796