P. Marín

Effect of Temperature on the Biotic Potential of Honeybee Microsporidia

ABSTRACT The biological cycle of Nosema spp. in honeybees depends on temperature. When expressed as total spore counts per day after infection, the biotic potentials of Nosema apis and N. ceranae at 33°C were similar, but a higher proportion of immature stages of N. ceranae than of N. apis were seen. At 25 and 37°C, the biotic potential of N. ceranae was higher than that of N. apis. The better adaptation of N. ceranae to complete its endogenous cycle at different temperatures clearly supports the observation of the different epidemiological patterns.

Magnetic hardening of FeSiBCuNb ribbons and wires during the first stage of crystallization to a nanophase structure

The structural and magnetic properties of Fe73.5Si13.5B9Cu1Nb3 alloy wire and ribbon have been studied after thermal treatments up to temperatures at which partial (75%) devitrification to a nanocrystalline structure occurs. Nanocrystals are detected by x‐ray diffraction only after treatments around 500u2009°C, while differential scanning calorimetry studies suggest that substantial structural change is inititiated at a much lower temperature (about 400°). A clear magnetic hardening is observed in samples heated within the temperature range 400–480u2009°C. This phenomenon is also accompanied by an increase of the linear magnetostriction. These effects are discussed in terms of the local structural rearrangements produced during the first stages of the crystallization process. The study is also extended partly to FeSiB, FeSiBCu, and FeSiBNb alloys.

Horizontal transmission of Nosema ceranae (Microsporidia) from worker honeybees to queens (Apis mellifera)

Horizontal transmission from worker honeybees to queens is confirmed in a laboratory essay as a possible route of Nosema ceranae infection in field colonies and pathological repercussions on honeybee queens are described. Lesions are only detected in the epithelial ventricular layer of the infected queens and death occurs within 3 weeks when the nurse workers are experimentally and collectively infected with approximately 5000 viable spores per bee. These data suggest that the higher number of infected house bees, the higher risk of transmission to queens. The presented data may explain the role of house honeybees in natural queen infection, although it is probably that a high proportion of infected house bees must be required to infect the queen.

Magnetism in nanoparticles: tuning properties with coatings

This paper reviews the effect of organic and inorganic coatings on magnetic nanoparticles. The ferromagnetic-like behaviour observed in nanoparticles constituted by materials which are non-magnetic in bulk is analysed for two cases: (a) Pd and Pt nanoparticles, formed by substances close to the onset of ferromagnetism, and (b) Au and ZnO nanoparticles, which were found to be surprisingly magnetic at the nanoscale when coated by organic surfactants. An overview of theories accounting for this unexpected magnetism, induced by the nanosize influence, is presented. In addition, the effect of coating magnetic nanoparticles with biocompatible metals, oxides or organic molecules is also reviewed, focusing on their applications.

Influence of Cr additions in magnetic properties and crystallization process of amorphous iron based alloys

Amorphous Fe63.5Cr10Si13.5B9Cu1Nb3 ribbon samples have been prepared by melt spinning. The addition of Cr to a FINEMET-type alloy decreases the Curie temperature of the amorphous matrix and also modifies the alloy crystallization temperature. The evolution of the microstructure during crystallization has been analyzed by means of x-ray diffractometry and transmission electron microscopy. An interesting dependence of the intensity of the amorphous diffraction halo was observed for temperatures below 818 K, where a large fraction of glassy phase was still present in the sample. The evolution of the coercivity with annealing temperature for various measurement temperatures has also been studied and, in conjunction with the microstructural observations, is interpreted within the framework of the two-phase theory for nanocrystalline materials.

Enhanced magnetic properties of FeCo ribbons nanocrystallized in magnetic field

Tailoring the structure of nanocrystalline microstructures is an important step toward controlled design of novel nanostructured materials and devices. We demonstrate how the nanocrystalline microstructure of Co-rich ribbons can be tuned by annealing under magnetic field. The intensity of the field allows controlling different degrees of order at annealing temperatures corresponding to the first stages of the nanocrystallization process. The energy barrier for nucleation is directionally affected by the applied field. The influence of grains assembling on exchange coupling between grains has been analyzed by means of magnetic domains observation and magnetic characterization by means of a hysteresis loop.

Natural infection by Nosema ceranae causes similar lesions as in experimentally infected caged-worker honey bees (Apis mellifera)

Summary In this report, the pathological features observed in honey bees naturally infected with the microsporidium Nosema ceranae throughout a year are described. The lesions produced under natural conditions are similar to those observed in experimentally caged worker honey bees. N. ceranae is able to reproduce inside epithelial cells and multiply all through the year causing lesions in host-cells, characterized by a progressive and irreversible destruction of the epithelial layer of the ventriculus, which can lead to major negative repercussions on the normal process of digestion, with critical consequences on honey bee and colony viability. It is remarkable that factors such as continuous access to fresh pollen around the apiary or temperature and humidity variations throughout the year in different seasons did not apparently influence the development of the endogenous cycle of this parasite under field conditions.

Magnetic field driving custom assembly in (FeCo) nanocrystals

We present the possibility of tuning the nanocrystalline microstructure of Co-rich samples by magnetic field annealing. Custom assembly of nucleated grains, aligned in the field direction, has been observed by means of high resolution transmission microscopy. The organized microstructure was obtained on the basis of the appropriate choice of composition, annealing temperature, related to the initial stages of nanocrystallization process, and magnetic field intensity. The linear pattern of the grains has been explained as a consequence of the counterbalance between magnetic, magnetostatic, and magnetocrystalline couplings, only relevant when the nucleation temperature is well below the Curie temperature of the nucleated phase.

Stress and field contactless sensor based on the scattering of electromagnetic waves by a single ferromagnetic microwire

In this paper, we report an experimental study on the microwave modulated scattering intensity for a single Fe_2.25Co_72.75Si_10B_15 amorphous metallic microwire. The modulation is driven by applying a bias magnetic field that tunes the magnetic permeability of the ferromagnetic microwire. Furthermore, by using a magnetostrictive microwire, we also demonstrate that the microwave scattering is sensitive to mechanical stresses. In fact, we present a wireless microwave controlled stress sensor, suitable for biological applications, as a possible use of this effect. In addition, a first order theoretical approximation accounts for the observed influence of the magnetic permeability on the scattering coefficients. That model leads to predictions in good agreement with the experimental results.

Magnetic hardening during the amorphous to nanocrystalline transformation in FeSiBCuNb alloys: theoretical considerations

Amorphous FeSiBCuNb alloy has been annealed up to 600°C giving structurally well-differentiated microstructures. The best soft magnetic properties have been found at 550°C annealed samples. Those annealed at 400°C, are soft magnetic. A relative magnetic hardening has been found in those heat-treated at 460°C with a low percentage of crystallised material and small grains (5 nm). The softening observed in 400°C annealed samples has been associated to the structural relaxation of the amorphous. In the 550°C annealed material the decrease of coercivity can be interpreted in terms of the smoothing part of the exchange interaction averaging out locally fluctuating anisotropies. The magnetic hardening at 460°C has been understood in terms of the increase of the magnetoelastic anisotropy.