2,555 research outputs found
Topology optimized permanent magnet systems
Topology optimization of permanent magnet systems consisting of permanent
magnets, high permeability iron and air is presented. An implementation of
topology optimization for magnetostatics is discussed and three examples are
considered. First, the Halbach cylinder is topology optimized with iron and an
increase of 15% in magnetic efficiency is shown, albeit with an increase of 3.8
pp. in field inhomogeneity - a value compared to the inhomogeneity in a 16
segmented Halbach cylinder. Following this a topology optimized structure to
concentrate a homogeneous field is shown to increase the magnitude of the field
by 111% for the chosen dimensions. Finally, a permanent magnet with alternating
high and low field regions is considered. Here a figure
of merit of 0.472 is reached, which is an increase of 100% compared to a
previous optimized design.Comment: 10 pages, 10 figure
The efficiency and the demagnetization field of a general Halbach cylinder
The maximum magnetic efficiency of a general multipole Halbach cylinder of
order is found as function of . The efficiency is shown to decrease for
increasing absolute value of . The optimal ratio between the inner and outer
radius, i.e. the ratio resulting in the most efficient design, is also found as
function of and is shown to tend towards smaller and smaller magnet sizes.
Finally, the demagnetizing field in a general -Halbach cylinder is
calculated, and it is shown that demagnetization is largest either at or . For the common case of a Halbach cylinder
the maximum values of the demagnetizing field is either at at
the outer radius, where the field is always equal to the remanence, or at at the inner radius, where it is the magnitude of the field in the
bore. Thus to avoid demagnetization the coercivity of the magnets must be
larger than these values.Comment: 5 pages, 5 figure
The lifetime cost of a magnetic refrigerator
The total cost of a 25 W average load magnetic refrigerator using commercial
grade Gd is calculated using a numerical model. The price of magnetocaloric
material, magnet material and cost of operation are considered, and all
influence the total cost. The lowest combined total cost with a device lifetime
of 15 years is found to be in the range \^{+++}$ refrigeration unit. In a
rough life time cost comparison between the magnetic refrigeration device and
such a unit we find similar costs, the former being slightly cheaper, assuming
the cost of the magnet can be recuperated at end of life.Comment: 17 pages, 17 figure
Brillouin Cooling
We analyze how to exploit Brillouin scattering for the purpose of cooling
opto-mechanical devices and present a quantum-mechanical theory for Brillouin
cooling. Our analysis shows that significant cooling ratios can be obtained
with standard experimental parameters. A further improvement of cooling
efficiency is possible by increasing the dissipation of the optical anti-Stokes
resonance.Comment: 4 pages 3 figure
Phylogeny of Rosellinia capetribulensis sp. nov. and its allies (Xylariaceae)
A new Rosellinia species, R. capetribulensis isolated from Calamus sp. in Australia is described. R. capetribulensis is characterized by perithecia immersed within a carbonaceous stroma surrounded by subiculum-like hyphae, asci with large, barrel-shaped amyloid apical apparatus and large dark brown spores. Morphologically, R. capetribulensis appears to be similar to R. bunodes, R. markhamiae and R. megalospora. To gain further insights into the phylogeny of this new taxon we analyzed the ITS-5.8S rDNA using maximum parsimony and likelihood methods. In addition, a morphological dataset also was analyzed phylogenetically to investigate possible affinities. ITS rDNA based phylogenies reveal that R. capetribulensis is closely related to other Rosellinia species showing closest affinity to R. arcuata, R. necatrix and R. pepo. However, analysis of R. capetribulensis forms an unsupported branch sister to these taxa. Results from the morphological matrix indicate a close morphological affinity to members of Rosellinia subgenus Rosellinia. Despite that ITS rDNA and morphological analyses present difficulties in constructing a proper phylogenetic framework among Rosellinia and allied genera, there is sufficient evidence to support the establishment of the new taxon in the genus Rosellinia. The morphological similarities and differences between R. capetribulensis and allied genera such as Astrocystis and Entoleuca are also briefly discussed.published_or_final_versio
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