2,267 research outputs found
Do we need MR conditional pacemakers?
Magnetic resonance imaging (MRI) is a widely accepted
tool for the diagnosis of a variety of disease states.
However, due to safety concerns the presence of an implanted
cardiac pacemaker is considered to be a contraindication
to MRI in most medical centres. The
increasing number of implanted pacemakers and the
estimated over 50% probability that a pacemaker patient
may be a candidate for an MRI increase the need
for safe scanning of pacemaker patients. Over the last
ten years a major effort has been made to understand
the potential risks. The influences from the three electromagnetic
fields on pacemakers are versatile and will
be summarised. The research in this area has helped to
predict the risks of an MRI scan in patients with conventional
pacemakers, and has also stimulated pacemaker
manufacturers to improve their devices with the
goal of providing MR conditional devices. Since autumn
2008 the first approved MR conditional pacemakers
have been on the market and other devices are likely to
follow this trend.
However, the vast majority of devices are still not
approved for MRI, a situation which will take several
years to change. It is thus important that a solution be
also found for these patients. Several studies including
over 500 patients with a pressing need for MRI have
been performed at different experienced centres. On
the basis of those data various organisations in MRI
fields have proposed guidelines for MRI in patients who
fulfill given requirements. However, at present, non-
MRI modalities should be considered, whenever possible,
for diagnosis in pacemaker recipients with conventional
devices. If other imaging modalities are not
adequate, MRI with careful monitoring and preparation
for adverse events may be considered only at experienced
centres. With the wider availability of MR
conditional devices, the risks of MRI are greatly reduced
and non-tertiary centres will be able to perform
these investigations. In any case, rapid progress in the
field of MR conditional pacing is desirable
Path integral for a relativistic Aharonov-Bohm-Coulomb system
The path integral for the relativistic spinless Aharonov-Bohm-Coulomb system
is solved, and the energy spectra are extracted from the resulting amplitude.Comment: 6 pages, Revte
Are Leaf Traits Suitable for Assessing the Feeding Value of Native Grass Species?
Research on forage feeding value other than in vivo assessment can be roughly divided into three kinds of approach. The first aims to predict feeding value using a set of enzymatic or physical methods. A second approach is based on phenological stages of species. These approaches are mainly used for pure stands of improved grasses or legumes. However, for native grassland, a complex type of vegetation, a third approach, based on botanical records, has been proposed to rank grassland communities for their feeding value. The aim of this work concerns the third approach. We tested whether leaf traits (e.g. specific leaf area (SLA), leaf dry matter content (LDMC) and leaf life span (LLS)), assessed under non-limiting plant growth conditions, ranked the species in the same order as did chemical components and digestibility
Centrifugal terms in the WKB approximation and semiclassical quantization of hydrogen
A systematic semiclassical expansion of the hydrogen problem about the
classical Kepler problem is shown to yield remarkably accurate results. Ad hoc
changes of the centrifugal term, such as the standard Langer modification where
the factor l(l+1) is replaced by (l+1/2)^2, are avoided. The semiclassical
energy levels are shown to be exact to first order in with all higher
order contributions vanishing. The wave functions and dipole matrix elements
are also discussed.Comment: 5 pages, to appear in Phys. Rev.
Application of extracts from the poisonous plant, Nerium Oleander L., as a wood preservative
The antifungal properties of poisonous plant extracts from oleanders (Nerium oleander L.) were determined when used as a wood preservative. The extract was prepared from oleanders leaves andflowers in 96% ethyl alcohol. The wood blocks of Turkish oriental beech (Fagus orientalis L.) and Scots pine (Pinus sylvestris L.) were impregnated with the extracts. The abilities of the extract to suppressattack by Postia placenta (Fr.) (brown rot) and Trametes versicolor (L: Fr.) Quel. (a white-rot) was investigated. Treated blocks were exposed to P. placenta and T. versicolor attacks for 12 weeks by following the soil-block method. While untreated wood specimens have weight loss ranging between 27.37 and 30.66% for P. placenta and 8.64 and 24.06% for T. versicolor, the wood treated with theextracts is of weight loss between 5.54 and 10.98% for P. placenta, and between 5.02 and 28.25% for T. versicolor. The lowest weight loss was found to be for beech wood (5.02%) impregnated with the extractof oleander at a concentration level of 0.25% against T. versicolor. While the highest weight loss was also on the beech wood (28.25%) treated with the same extract at the level of 0.50% concentrationagainst T. versicolor. In conclusion, the extracts could be used as effective wood preservative
Coarse-grained computations of demixing in dense gas-fluidized beds
We use an "equation-free", coarse-grained computational approach to
accelerate molecular dynamics-based computations of demixing (segregation) of
dissimilar particles subject to an upward gas flow (gas-fluidized beds). We
explore the coarse-grained dynamics of these phenomena in gently fluidized beds
of solid mixtures of different densities, typically a slow process for which
reasonable continuum models are currently unavailable
Introduction and evaluation of the wood preservative potentials of the poisonous Sternbergia candidum extracts
The ability of Sternbergia candida (SB Candidum Mathew.) extract to suppress attack by Postia placenta (Fries) M. Larsen et Lombard (Mad 698), (a brown-rot) and Trametes versicolor (L.ex Fr.) Quel.(a white-rot) was investigated. The extract was dissolved from Sterinbergia Candidum’s bulb and leaves in 96% ethyl alcohol. Poisonous extract impregnated into wood blocks of Turkish oriental beech (Fagus orientalis L.) and Scots pine (Pinus sylvestris L.). Extract dosages were 0.25, 0.75, 1.50 and 3.00%. Treated blocks were exposed to P. placenta and T. versicolor attack for 12 weeks by the soil block method. Only extract dosages of 0.25 and 0.75% were found efficacious in suppressing attack. A tukey studentized test found both dosages significant at 5% level. In conclusion, the poisonous extracts could be used as effective wood preservative when concentration was adjusted
A case study of a density structure over a vertical magnetic field region in the Martian ionosphere
One of the discoveries made by the radar sounder on the Mars Express spacecraft is the existence of magnetically controlled structures in the ionosphere of Mars, which result in bulges in the ionospheric electron density contours. These bulges lead in turn to oblique echoes, which show up as hyperbola-shaped features in the echograms. A hyperbola-shaped feature observed over an isolated region of strong crustal magnetic field is associated with a plasma cavity in the upper ionosphere and a corresponding density enhancement in the lower levels of the ionosphere. We suggest that along open magnetic field lines, the solar wind electrons are accelerated downward and the ionospheric ions are accelerated upward in a manner similar to the field line-driven auroral acceleration at Earth. This heating due to precipitating electrons may cause an increase in the scale height and may drive a loss of ionospheric plasma at high altitudes
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