836 research outputs found
Magnetic nanocomposites at microwave frequencies
Most conventional magnetic materials used in the electronic devices are
ferrites, which are composed of micrometer-size grains. But ferrites have small
saturation magnetization, therefore the performance at GHz frequencies is
rather poor. That is why functionalized nanocomposites comprising magnetic
nanoparticles (e.g. Fe, Co) with dimensions ranging from a few nm to 100 nm,
and embedded in dielectric matrices (e.g. silicon oxide, aluminium oxide) have
a significant potential for the electronics industry. When the size of the
nanoparticles is smaller than the critical size for multidomain formation,
these nanocomposites can be regarded as an ensemble of particles in
single-domain states and the losses (due for example to eddy currents) are
expected to be relatively small. Here we review the theory of magnetism in such
materials, and we present a novel measurement method used for the
characterization of the electromagnetic properties of composites with
nanomagnetic insertions. We also present a few experimental results obtained on
composites consisting of iron nanoparticles in a dielectric matrix.Comment: 20 pages, 10 figures, 5 table
Aeolian sans ripples: experimental study of saturated states
We report an experimental investigation of aeolian sand ripples, performed
both in a wind tunnel and on stoss slopes of dunes. Starting from a flat bed,
we can identify three regimes: appearance of an initial wavelength, coarsening
of the pattern and finally saturation of the ripples. We show that both initial
and final wavelengths, as well as the propagative speed of the ripples, are
linear functions of the wind velocity. Investigating the evolution of an
initially corrugated bed, we exhibit non-linear stable solutions for a finite
range of wavelengths, which demonstrates the existence of a saturation in
amplitude. These results contradict most of the models.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Lett. Title changed,
figures corrected and simplified, more field data included, text clarifie
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Tomographic wavefront correction for the LSST
The Large Synoptic Survey Telescope (LSST) is a three mirror modified Paul-Baker design with an 8.4m primary, a 3.4m secondary, and a 5.0m tertiary followed by a 3-element refractive corrector producing a 3.5 degree field of view. This design produces image diameters of <0.3 arcsecond 80% encircled energy over its full field of view. The image quality of this design is sufficient to ensure that the final images produced by the telescope will be limited by the atmospheric seeing at an excellent astronomical site. In order to maintain this image quality, the deformations and rigid body motions of the three large mirrors must be actively controlled to minimize optical aberrations. By measuring the optical wavefront produced by the telescope at multiple points in the field, mirror deformations and rigid body motions that produce a good optical wavefront across the entire field may be determined. We will describe the details of the techniques for obtaining these solutions. We will show that, for the expected mirror deformations and rigid body misalignments, the solutions that are found using these techniques produce an image quality over the field that is close to optimal. We will discuss how many wavefront sensors are needed and the tradeoffs between the number of wavefront sensors, their layout and noise sensitivity
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LSST Camera Optics
The Large Synoptic Survey Telescope (LSST) is a unique, three-mirror, modified Paul-Baker design with an 8.4m primary, a 3.4m secondary, and a 5.0m tertiary feeding a camera system that includes corrector optics to produce a 3.5 degree field of view with excellent image quality (<0.3 arcsecond 80% encircled diffracted energy) over the entire field from blue to near infra-red wavelengths. We describe the design of the LSST camera optics, consisting of three refractive lenses with diameters of 1.6m, 1.0m and 0.7m, along with a set of interchangeable, broad-band, interference filters with diameters of 0.75m. We also describe current plans for fabricating, coating, mounting and testing these lenses and filters
Quasi-static cracks and minimal energy surfaces
We compare the roughness of minimal energy(ME) surfaces and scalar
``quasi-static'' fracture surfaces(SQF). Two dimensional ME and SQF surfaces
have the same roughness scaling, w sim L^zeta (L is system size) with zeta =
2/3. The 3-d ME and SQF results at strong disorder are consistent with the
random-bond Ising exponent zeta (d >= 3) approx 0.21(5-d) (d is bulk
dimension). However 3-d SQF surfaces are rougher than ME ones due to a larger
prefactor. ME surfaces undergo a ``weakly rough'' to ``algebraically rough''
transition in 3-d, suggesting a similar behavior in fracture.Comment: 7 pages, aps.sty-latex, 7 figure
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The use of an intermediate wavelength laser for alignment to inertial confinement fusion targets
The conceptual design of the National Ignition Facility (NIF) 192 beam laser incorporates a low-power alignment beam injected in the pinhole plane of the final spatial filter with a wave length intermediate between the 1053 mn laser output and the 351 mn frequency-converted beam that illuminates the target Choosing the specific wavelength for which the spatial filter plane is reimaged in the same target chamber plane as the frequency-converted main laser pulse, achieves optimum accuracy without the need for additional means to insure precise overlap between the two beams. Insertion of the alignment beam after the last laser amplifier also allows alignment to the target while the amplifiers are still cooling from a previous shot
Retrospective evidence for a biological cost of vancomycin resistance determinants in the absence of glycopeptide selective pressures
To estimate the relative fitness differences between glycopeptide-resistant Enterococcus faecium (GREF) and glycopeptide-susceptible E. faecium (GSEF) from yearly surveillance data on the occurrence of GREF in Danish poultry farm environments.
A population genetic model was adapted to retrospectively estimate the biological fitness cost of acquired resistance. Maximization of a likelihood function was used to predict the longitudinal persistence of acquired resistance.
Our analysis suggests strong selection against GREF following the 1995 ban on the glycopeptide growth promoter avoparcin. However, parameterizing the model with two selection coefficients suggesting a reduced negative effect of the acquired resistance on bacterial fitness over time significantly improved the fit of the model. Our analyses suggest that the acquired glycopeptide resistance will persist for >25 years.
Conclusions Acquired resistance determinants in commensal E. faecium populations in Danish farm environments are likely to persist for decades, even in the absence of glycopeptide use
International Veterinary Epilepsy Task Force consensus report on epilepsy definition, classification and terminology in companion animals
Dogs with epilepsy are among the commonest neurological patients in veterinary practice and therefore have historically attracted much attention with regard to definitions, clinical approach and management. A number of classification proposals for canine epilepsy have been published during the years reflecting always in parts the current proposals coming from the human epilepsy organisation the International League Against Epilepsy (ILAE). It has however not been possible to gain agreed consensus, “a common language”, for the classification and terminology used between veterinary and human neurologists and neuroscientists, practitioners, neuropharmacologists and neuropathologists. This has led to an unfortunate situation where different veterinary publications and textbook chapters on epilepsy merely reflect individual author preferences with respect to terminology, which can be confusing to the readers and influence the definition and diagnosis of epilepsy in first line practice and research studies.
In this document the International Veterinary Epilepsy Task Force (IVETF) discusses current understanding of canine epilepsy and presents our 2015 proposal for terminology and classification of epilepsy and epileptic seizures. We propose a classification system which reflects new thoughts from the human ILAE but also roots in former well accepted terminology. We think that this classification system can be used by all stakeholders
A report on the health and social care listening event
The purpose of the Listening Event was to enable a wide range of people, including professionals working in statutory, voluntary and other organisations and members of the public, to ‘have a say’ about health and social care and what we as a University can do for and with these partners and the public. We particularly wanted to hear about key concerns of the University such as:
• Strengthening community engagement and partnerships
• Health and social care training we should be providing, for whom, and how this is delivered
• Ideas relating to the University themes including media, use of space and buildings, human rights, social justice and security
• Research topics we should be addressing
However the main strength of the Listening Event approach is that topics for discussion are mostly led by participants who attend. On this occasion, the
discussion topics were very much focused on the concerns of participants and lots of information and ideas were generated. The task now is for the event planning team to review the discussion notes and identify what can be
addressed and how, in the short, medium and long term. This planning will be taking place over the Autumn in 2011, and any participants or readers of this report are more than welcome to get in touch to work with us or add their views.
The purpose of this report is to record all discussion summaries for sharing amongst participants and others. It is important that participants especially get to read what others had said at the event. The report will lead to changes in University practices such as the content of some of our courses and new business ideas and relationships will also be explored. The event itself provided a useful means of public engagement that others may wish to adopt
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