696 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
Impalement transitions in droplets impacting microstructured superhydrophobic surfaces
Liquid droplets impacting a superhydrophobic surface decorated with
micro-scale posts often bounce off the surface. However, by decreasing the
impact velocity droplets may land on the surface in a fakir state, and by
increasing it posts may impale droplets that are then stuck on the surface. We
use a two-phase lattice-Boltzmann model to simulate droplet impact on
superhydrophobic surfaces, and show that it may result in a fakir state also
for reasonable high impact velocities. This happens more easily if the surface
is made more hydrophobic or the post height is increased, thereby making the
impaled state energetically less favourable.Comment: 8 pages, 4 figures, to appear in Europhysics Letter
Ferromagnetic resonance in -Co magnetic composites
We investigate the electromagnetic properties of assemblies of nanoscale
-cobalt crystals with size range between 5 nm to 35 nm, embedded in a
polystyrene (PS) matrix, at microwave (1-12 GHz) frequencies. We investigate
the samples by transmission electron microscopy (TEM) imaging, demonstrating
that the particles aggregate and form chains and clusters. By using a broadband
coaxial-line method, we extract the magnetic permeability in the frequency
range from 1 to 12 GHz, and we study the shift of the ferromagnetic resonance
with respect to an externally applied magnetic field. We find that the
zero-magnetic field ferromagnetic resonant peak shifts towards higher
frequencies at finite magnetic fields, and the magnitude of complex
permeability is reduced. At fields larger than 2.5 kOe the resonant frequency
changes linearly with the applied magnetic field, demonstrating the transition
to a state in which the nanoparticles become dynamically decoupled. In this
regime, the particles inside clusters can be treated as non-interacting, and
the peak position can be predicted from Kittel's ferromagnetic resonance theory
for non-interacting uniaxial spherical particles combined with the
Landau-Lifshitz-Gilbert (LLG) equation. In contrast, at low magnetic fields
this magnetic order breaks down and the resonant frequency in zero magnetic
field reaches a saturation value reflecting the interparticle interactions as
resulting from aggregation. Our results show that the electromagnetic
properties of these composite materials can be tuned by external magnetic
fields and by changes in the aggregation structure.Comment: 14 pages, 13 figure
Archaea are prominent members of the prokaryotic communities colonizing common forest mushrooms
In this study, the abundance and composition of prokaryotic communities associated with the inner tissue of fruiting bodies of Suillus bovinus, Boletus pinophilus, Cantharellus cibarius, Agaricus arvensis, Lycoperdon perlatum, and Piptoporus betulinus were analyzed using culture-independent methods. Our findings indicate that archaea and bacteria colonize the internal tissues of all investigated specimens and that archaea are prominent members of the prokaryotic community. The ratio of archaeal 16S rRNA gene copy numbers to those of bacteria was >1 in the fruiting bodies of four out of six fungal species included in the study. The largest proportion of archaeal 16S rRNA gene sequences belonged to thaumarchaeotal classes Terrestrial group, Miscellaneous Crenar-chaeotic Group (MCG), and Thermoplasmata. Bacterial communities showed characteristic compositions in each fungal species. Bacterial classes Gammaproteobacteria, Actinobacteria, Bacilli, and Clostridia were prominent among communities in fruiting body tissues. Bacterial populations in each fungal species had different characteristics. The results of this study imply that fruiting body tissues are an important habitat for abundant and diverse populations of archaea and bacteria.Peer reviewe
Europe’s Care Regimes and the Role of Migrant Care Workers Within Them
This paper is an examination of the recent restructuring and subsequent convergence of European long-term care models. This paper also aims to highlight the increased role of migrant care workers and the need for great social and governmental recognition for all care providers. The provision of long term care is complex, divided between state, market and family providers; the state alone could not and does not act as the sole provider of care (Banks 1998). The extent to which different sectors are relied upon is largely dependent on the ideology of the country's welfare state (Timonen and Doyle 2007)
Scaling Exponents in the Incommensurate Phase of the Sine-Gordon and U(1) Thirring Models
In this paper we study the critical exponents of the quantum sine-Gordon and
U(1) Thirring models in the incommensurate phase. This phase appears when the
chemical potential exceeds a critical value and is characterized by a
finite density of solitons. The low-energy sector of this phase is critical and
is described by the Gaussian model (Tomonaga-Luttinger liquid) with the
compactification radius dependent on the soliton density and the sine-Gordon
model coupling constant .
For a fixed value of , we find that the Luttinger parameter is
equal to 1/2 at the commensurate-incommensurate transition point and approaches
the asymptotic value away from it. We describe a possible phase
diagram of the model consisting of an array of weakly coupled chains. The
possible phases are Fermi liquid, Spin Density Wave, Spin-Peierls and Wigner
crystal.Comment: 10pages; Improved version; Submitted to Physical Review
Efficient DNA fingerprinting of Clostridium botulinum types A, B, E, and F by amplified fragment length polymorphism analysis.
Amplified fragment length polymorphism (AFLP) analysis was applied to characterize 33 group I and 37 group II Clostridium botulinum strains. Four restriction enzyme and 30 primer combinations were screened to tailor the AFLP technique for optimal characterization of C. botulinum. The enzyme combination HindIII and HpyCH4IV, with primers having one selective nucleotide apiece (Hind-C and Hpy-A), was selected. AFLP clearly differentiated between C. botulinum groups I and II; group-specific clusters showed <10% similarity between proteolytic and nonproteolytic C. botulinum strains. In addition, group-specific fragments were detected in both groups. All strains studied were typeable by AFLP, and a total of 42 AFLP types were identified. Extensive diversity was observed among strains of C. botulinum type E, whereas group I had lower genetic biodiversity. These results indicate that AFLP is a fast, highly discriminating, and reproducible DNA fingerprinting method with excellent typeability, which, in addition to its suitability for typing at strain level, can be used for C. botulinum group identification
Identification of Clostridium species and DNA fingerprinting of Clostridium perfringens by amplified fragment length polymorphism analysis
An amplified fragment length polymorphism (AFLP) method was applied to 129 strains representing 24 different Clostridium species, with special emphasis on pathogenic clostridia of medical or veterinary interest, to assess the potential of AFLP for identification of clostridia. In addition, the ability of the same AFLP protocol to type clostridia at the strain level was assessed by focusing on Clostridium perfringens strains. All strains were typeable by AFLP, so the method seemed to overcome the problem of extracellular DNase production. AFLP differentiated all Clostridium species tested, except for Clostridium ramosum and Clostridium limosum, which clustered together with a 45% similarity level. Other Clostridium species were divided into species-specific clusters or occupied separate positions. Wide genetic diversity was observed among Clostridium botulinum strains, which were divided into seven species-specific clusters. The same AFLP protocol was also suitable for typing C. perfringens at the strain level. A total of 29 different AFLP types were identified for 37 strains of C. perfringens; strains initially originating from the same isolate showed identical fingerprinting patterns and were distinguished from unrelated strains. AFLP proved to be a highly reproducible, easy-to-perform, and relatively fast method which enables high throughput of samples and can serve in the generation of identification libraries. These results indicate that the AFLP method provides a promising tool for the identification and characterization of Clostridium species
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