4,771 research outputs found
Particle acceleration in tangential discontinuities by lower hybrid waves
We consider the role that the lower-hybrid wave turbulence plays in providing the necessary resistivity at collisionless reconnection sights. The mechanism for generating the waves is considered to be the lower-hybrid drift instability. We find that the level of the wave amplitude is sufficient enough to heat and accelerate both electrons and ions
Robust active magnetic dearing control using stabilizing dynamical compensators
The robust control of active magnetic bearings, based on a linearised interval model, is considered. Through robust stability analysis, all the first-order robust stabilizing dynamical compensators for the interval system are obtained. Disturbance attenuation and minimum control effort are also addressed. The approach is applied to a high-speed flywheel supported by two active and two passive magnetic bearings. Simulation and experimental results both show that it is simple, effective, and robust
Robust magnetic bearing control using stabilizing dynamical compensators
AbstractâThis paper considers the robust control of an active radial magnetic bearing system, having a homopolar, external rotor topology, which is used to support an annular fiber composite flywheel rim. A first-order dynamical compensator, which uses only position feedback information, is used for control, its design being based on a linearized one-dimensional second-order model which is treated as an interval system in order to cope with parameter uncertainties. Through robust stability analysis, a parameterization of all first-order robustly stabilizing dynamical compensators for the interval system is initially obtained. Then, by appropriate selection of the free parameters in the robust controller, the H2 norm of the disturbance-output transfer function is made arbitrarily small over the system parameter intervals, and the norm of the inputâoutput transfer function is made arbitrarily close to a lower bound. Simulation and experimental
results demonstrate both stability and performance robustness of the developed controller
Analysis of self-oscillating DC-DC resonant power converters using a hysteretic relay
The paper presents a technique for exciting resonant DC-DC converters in a self-oscillating manner. The analysis necessary to predict the behaviour of such converters is also given. The oscillation is based on the behaviour of a hysteretic relay with a negative hysteresis transition. Self-oscillating converters benefit from higher efficiency/higher power density than their non-self-oscillating counterparts as they can be operated closer to the tank resonant frequency. The self-oscillating mechanism presented here is also simple and cost effective to implement. A prototype converter is presented in order to verify the theoretical claims
SIRIS: a high resolution scanning infrared camera for examining paintings
The new SIRIS (Scanning InfraRed Imaging System) camera developed at the National Gallery in London allows highresolution images of paintings to be made in the near infrared region (900â1700 nm). Images of 5000 Ă 5000 pixels are made by moving a 320 Ă 256 pixel InGaAs array across the focal plane of the camera using two orthogonal translation stages. The great advantages of this camera over scanning infrared devices are its relative portability and that image acquisition is comparatively rapid â a full 5000 Ă 5000 pixel image can be made in around 20 minutes. The paper describes the development of the mechanical, optical and electronic components of the camera, including the design of a new lens. The software routines used to control image capture and to assemble the individual 320 Ă 256 pixel frames into a seamless mosaic image are also mentioned. The optics of the SIRIS camera have been designed so that the camera can operate at a range of resolutions; from around 2.5 pixels per millimetre on large paintings of up to 2000 Ă 2000 mm to 10 pixels per millimetre on smaller paintings or details of paintings measuring 500 Ă 500 mm. The camera is primarily designed to examine underdrawings in paintings; preliminary results from test targets and paintings are presented and the quality of the images compared with those from other cameras currently used in this field
Designing fractional factorial split-plot experiments with few whole-plot factors
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73673/1/j.1467-9876.2003.05029.x.pd
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Impact Absorbent Rapid Manufactured Structures (IARMS)
Rapid Manufacturing (RM) is increasingly becoming a viable manufacturing process due
to dramatic advantages that it facilitates in the area of design complexity. Through the
exploration of the design freedom afforded by RM, this paper introduces the concept and initial
research surrounding Impact Absorbent Rapid Manufactured Structures (IARMS), with an
application in sports personal protective equipment (PPE). Designs are based on the cellular
structure of foams; the inherent advantages of the cellular structure are used as a basis to create
IARMS that have the potential to be optimised for a specific impact absorbent response. The
paper provides some initial results from compression testingMechanical Engineerin
Undulation instability in a bilayer lipid membrane due to electric field interaction with lipid dipoles
Bilayer lipid membranes [BLMs] are an essential component of all biological
systems, forming a functional barrier for cells and organelles from the
surrounding environment. The lipid molecules that form membranes contain both
permanent and induced dipoles, and an electric field can induce the formation
of pores when the transverse field is sufficiently strong (electroporation).
Here, a phenomenological free energy is constructed to model the response of a
BLM to a transverse static electric field. The model contains a continuum
description of the membrane dipoles and a coupling between the headgroup
dipoles and the membrane tilt. The membrane is found to become unstable through
buckling modes, which are weakly coupled to thickness fluctuations in the
membrane. The thickness fluctuations, along with the increase in interfacial
area produced by membrane buckling, increase the probability of localized
membrane breakdown, which may lead to pore formation. The instability is found
to depend strongly on the strength of the coupling between the dipolar
headgroups and the membrane tilt as well as the degree of dipolar ordering in
the membrane.Comment: 29 pages 8 fig
Instabilities in neutrino-plasma density waves
One examines the interaction and possible resonances between supernova
neutrinos and electron plasma waves. The neutrino phase space distribution and
its boundary regions are analyzed in detail. It is shown that the boundary
regions are too wide to produce non-linear resonant effects. The growth or
damping rates induced by neutrinos are always proportional to the neutrino flux
and .Comment: 9 pages, a few words modified to match PRD publicatio
Fit Fans: perspectives of a practitioner and understanding participant health needs within a health promotion programme for older men delivered within an English Premier League Football Club
Fit Fans was a menâs health promotion intervention delivered within an English Premier League Football Club (2010â2011), which aimed to support the local community dwelling older men in lifestyle promotion (physical activity [PA], diet and well-being). The purpose of this study was to provide a reflexive account of a practitioner and the needs of participants. Seven men (mean age 58âyears) attended weekly PA and lifestyle sessions over an eight-month period. Baseline physiological measurements included body mass index, resting blood pressure and abdominal girth. Principles of ethnography and observational research (i.e. field notes, reflective diary) were adopted by the practitioner. Unexpectedly, the cohort exhibited a range of serious diagnosed illnesses that challenged the practitionerâs skill base and experience in the delivery of the intervention. Reflections of the practitioner and the stories of the progression that participants made add insight to future football in the community programmes
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