Equations of Motion and Frequency Dependence of Magnon-Induced Domain Wall Motion

Spin waves can induce domain wall motion in ferromagnets. We derive the equations of motion for a transverse domain wall driven by spin waves. Our calculations show that the magnonic spin-transfer torque does not cause rotation-induced Walker breakdown. The amplitude of spin waves that are excited by a localized microwave field depends on the spatial profile of the field and the excitation frequency. By taking this frequency dependence into account, we show that a simple one-dimensional model may reproduce much of the puzzling frequency dependence observed in early numerical studies.Comment: 7 pages, 7 figure

The Intrinsic Magnetization of Antiferromagnetic Textures

Antiferromagnets (AFMs) exhibit intrinsic magnetization when the order parameter spatially varies. This intrinsic spin is present even at equilibrium and can be interpreted as a twisting of the homogeneous AFM into a state with a finite spin. Because magnetic moments couple directly to external magnetic fields, the intrinsic magnetization can alter the dynamics of antiferromagnetic textures under such influence. Starting from the discrete Heisenberg model, we derive the continuum limit of the free energy of AFMs in the exchange approximation and explicitly rederive that the spatial variation of the antiferromagnetic order parameter is associated with an intrinsic magnetization density. We calculate the magnetization profile of a domain wall and discuss how the intrinsic magnetization reacts to external forces. We show conclusively, both analytically and numerically, that a spatially inhomogeneous magnetic field can move and control the position of domain walls in AFMs. By comparing our model to a commonly used alternative parametrization procedure for the continuum fields, we show that the physical interpretations of these fields depend critically on the choice of parametrization procedure for the discrete-to-continuous transition. This can explain why a significant amount of recent studies of the dynamics of AFMs, including effective models that describe the motion of antiferromagnetic domain walls, have neglected the intrinsic spin of the textured order parameter.Comment: 12 pages, 7 figure

Staggered Dynamics in Antiferromagnets by Collective Coordinates

Antiferromagnets can be used to store and manipulate spin information, but the coupled dynamics of the staggered field and the magnetization are very complex. We present a theory which is conceptually much simpler and which uses collective coordinates to describe staggered field dynamics in antiferromagnetic textures. The theory includes effects from dissipation, external magnetic fields, as well as reactive and dissipative current-induced torques. We conclude that, at low frequencies and amplitudes, currents induce collective motion by means of dissipative rather than reactive torques. The dynamics of a one-dimensional domain wall, pinned at 90$^{\circ}$ at its ends, are described as a driven harmonic oscillator with a natural frequency inversely proportional to the length of the texture.Comment: 4 pages, 2 figure

The social construction of female engineers : a qualitative case study of engineering education

This research is a case study of three important phases of engineering education: the social factors influencing young women and men in choosing engineering as a profession, what causes students to discontinue their studies, and the students' educational, social and cultural experiences during their education. The study is within the framework of feminist standpoint epistemology and uses both qualitative and quantitative methods, giving the study both depth and breadth. The data derive from a demographic survey of one first-year cohort in an engineering college, from non-participant observations in first, third, and fourth-year engineering classes, but primarily from in-depth, tape-recorded interviews with male and female students at the first and fourth year levels of study and with students who transferred to other disciplines. Data collection took place between September, 1996 and April, 1998. Major findings point to a chilly climate in the college of engineering where a masculine culture tends to exclude the female students from equal and equitable educational experiences. This culture, which in addition to exclusionary features includes a heavy workload with little time left for outside activities, was a major reason for attrition from the engineering program. There are also indications of an environment where male harassment of female students cause significant discomfort to women. However, women's attempts to voice their objection to such treatment are met with further exaggeration of the problem. The women are also labelled as troublemakers, poor sports, poor team-players, and lacking a sense of humour. The college exploited a committee of female students as volunteers in its recruitment strategy. This committee earned high praise from the administrative level, having raised the ratio of first-year female students from 5% to 22% at the same time as the college increased enrollment limit from 300 to 410 students. However, it had low prestige among the students. This research is significant in its use of feminist theory and methodology and using a qualitative method that allows the students own words and voices to express their day-to-day, lived experiences in the college

Magnetic susceptibility of vanadium carbide

Magnetic susceptibility of vanadium carbide from 77 to 300 K measured by magnetomete

Medical emergencies on large passenger ships without doctors: the Oslo-Kiel-Oslo ferry experience

Background: The Oslo-Kiel-Oslo route is currently the only direct ferry crossing between Norway and Germany, covered by 2 cruise-and-cars ferries carrying about 2,600 passengers each and sailing every day (20 h at sea, 4 h in port). Unlike most ocean going cruise vessels, they are not required to carry a physician but an on-board paramedic handles medical emergencies. The aim of the study was to provide data on medical emergencies leading to helicopter evacuations (helivacs) or other urgent transfers to facilities ashore from the two ferries during a 3-year period. Materials and methods: Data about the ferries, passengers, crew, helivacs and other medical transfers were collected from official company statistics and the paramedics’ transfer reports. Results: A total of 169 persons, including 14 (8.3%) crewmembers, were transferred from the ferries to land-based facilities by ambulance while alongside (n = 80; 47.3%) or evacuated by helicopter (n = 85; 50.3%) and rescue boat (n = 4; 2.4%) during the 3-year period. Transfer destinations were Denmark (n = 53), Germany (n = 49), Norway (n = 48) and Sweden (n = 19). The passenger helivac rate was 2.4 per 100,000 passenger-days. One person was airlifted from a ferry every 2 weeks. Among helivacs, 40% were heart-related, and more cardiac cases were airlifted than transferred by ambulance in port. Conclusions: All helivac requests were made after discussion between the ferry’s paramedic and telemedical doctors ashore and agreement that the medical challenge exceeded the ferry’s capability. This close cooperation kept the threshold for arranging helivacs from the ferries low, enabling short transport times to land-based facilities for critically ill patients. Further studies, including feedback from the receiving hospitals, are needed to determine measures that can reduce possible helicopter overutilisation without compromising patient safety and outcome.