ABSTRACT:In modern magnetic resonance imaging (MRI), patients are exposed to strong, rapidly switching magnetic gradient fields that, in extreme cases, may be able to elicit nerve stimulation. This paper presents theoretical investigations into the spatial distribution of induced current inside human tissues caused by pulsed z-gradient fields. A variety of gradient waveforms have been studied. The simulations are based on a new, high-definition, finite-difference time-domain method and a realistic inhomogeneous 10-mm resolution human body model with appropriate tissue parameters. It was found that the eddy current densities are affected not only by the pulse sequences but by many parameters such as the position of the body inside the gradient set, the local biological material properties and the geometry of the body. The discussion contains a comparison of these results with previous results found in the literature. This study and the new methods presented herein will help to further investigate the biological effects caused by the switched gradient fields in a MRI scan.

An inverse methodology is described to assist in the design of radio-frequency (RF) coils for magnetic resonance imaging (MRI) applications. The time-harmonic electromagnetic Green's functions are used to calculate current on the coil and shield cylinders that will generate a specified internal magnetic field. Stream function techniques and the method of moments are then used to implement this theoretical current density into an RF coil. A novel asymmetric coil operating for a 4.5 T MRI machine was designed and constructed using this methodology and the results are presented.

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Summary In the autumn of 1902 the Wright brothers spent just over eight weeks at their test site in the Kill Devil Hills near Kitty Hawk, North Carolina, testing their third Glider design. During the trial period they implemented an inter-linked roll-yaw control system. Together with the forward canard surface, this gave them control over vertical and horizontal components of the flight path. They were also able to hone and perfect their piloting skills. In just two days in the final week, they made about 250 glides. The success of the trials instilled the confidence in the Wright brothers to proceed rapidly to the construction of a powered aircraft. Within a month of returning to Dayton, they were writing to engine manufacturers with their specification – an engine that would develop eight to nine brake horse power, weigh no more than 180lb and be free from vibration; they would not find a suitable powerplant and had to design and build their own. The invention of the powered aeroplane in 1903 somewhat overshadows the earlier critical flight control developments, but the birth of flight control in 1902 opened the way for aviation to flourish. With the aid of modern flight science techniques – wind-tunnel testing, computational flight dynamics and piloted simulation, this paper examines the technology of the Wrights' 1902 glider. The research forms a part of the Liverpool Wright Project, aiming to bring to life the Wright brothers' achievements in this centenary period. Wilbur and Orville Wright are recognised by many as the first aeronautical engineers and test pilots. In so many ways they set standards that today's engineers and organisations benefit from. Their work in the period 1901 to 1902 reflects their genius and the paper reviews this work in detail, examining the design, aerodynamic characteristics and flying qualities of the aircraft that first featured a practical three-axis control system.

Over the past decade, NASA, under a succession of rotary-wing programs, has been moving towards coupling multiple discipline analyses to evaluate rotorcraft conceptual designs. Handling qualities is one of the component analyses to be included in such a future Multidisciplinary Analysis and Optimization framework for conceptual design of Vertical Take-Off and Landing (VTOL) aircraft. Similarly, the future vision for the capability of the Concept Design and Assessment Technology Area of the U.S Army Aviation Development Directorate also includes a handling qualities component. SIMPLI-FLYD is a tool jointly developed by NASA and the U.S. Army to perform modelling and analysis for the assessment of the handling qualities of rotorcraft conceptual designs. Illustrative scenarios of a tiltrotor in forward flight and a single-main rotor helicopter at hover are analysed using a combined process of SIMPLI-FLYD integrated with the conceptual design sizing tool NDARC. The effects of variations of input parameters such as horizontal tail and tail rotor geometry were evaluated in the form of margins to fixed- and rotary-wing handling qualities metrics and the computed vehicle empty weight. The handling qualities Design Margins are shown to vary across the flight envelope due to both changing flight dynamics and control characteristics and changing handling qualities specification requirements. The current SIMPLI-FLYD capability, lessons learned from its use and future developments are discussed.