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.Biotic potential represents the maximum reproductive capacity of a population under optimum environmental conditions. Thus, a species fulfilling its biotic potential would exhibit maximal exponential population growth, thereby augmenting the possibilities of transmission of the species. A wide range of factors affects the biotic potential of each species, and among the external factors, temperature clearly influences the life cycles of most parasitic species (4).Nosemosis is a common worldwide disease of adult honeybees (Apis mellifera) that is caused by microsporidia (19). Nosema apis was the only agent known to produce this disease in A. mellifera until N. ceranae was identified in this host in 2005, in Europe (11) and Taiwan (12). Both these microsporidia infect and multiply in the ventricular cells of A. mellifera, and they can be found under different environmental conditions in both the northern and southern hemispheres (17, 13). Significantly, N. ceranae seems to be more pathogenic than N. apis in caged worker bees (10, 18), and it has recently been related to significant losses of bees and colony collapses under field conditions (17,8).Due to the lack of comparative studies of the factors affecting parasite virulence, trials were designed to determine the influence of temperature on the biotic potentials of both microsporidia. Only the deleterious effect of high exogenous temperature on spores of N. apis has been checked previously (16).In this work, purified N. apis and N. ceranae spores with a minimum viability of 99% (tested with 4% trypan blue) were obtained from experimentally infected honeybees always maintained at 33°C as described previously (9). The spores were counted using a hemocytometer chamber (19), while the Nosema species identification was confirmed by PCR (17).The experimental infection of bees was carried out as described previously (10). Briefly, young Nosema-free honeybees were starved for 2 h and fed 2 l of 50% sucrose solution containing 100,000 viable N. ceranae or N. apis spores. Honeybees were anesthetized with CO 2 , and later, a droplet of the spore solution was administered to each honeybee by touching a micropipette to its mouthparts until the entire droplet was consumed. The bees that did not consume the entire droplet were discarded. Uninfected control bees were fed 2 l of 50% sucrose solution alone.Three trials were carried out for 1 week each at three different temperatures (25, 33, and 37°C). Each trial included four replicate cages ...

The giant magneto-impedance effect ͑GMI͒ is studied as a function of the structural modification induced in an Fe 73.5 Si 13.5 B 9 Cu 1 Nb 3 amorphous alloy wire by annealing. The values of GMI are correlated to those structural changes and with the corresponding variation of the magnetic properties and intrinsic resistivity. Excellent soft magnetic properties, associated with low resistivity values, make this nanostructured material as one of the most promising for future applications of the GMI effect. The tailoring of the structure which can be induced by adequate thermal treatments easily allows one to obtain excellent combinations of circumferential permeability and resistivity during different devitrification stages, in order to produce materials for specific aims. Maximum GMI ratios of 200% are found after annealing the wires in the range 550-600°C, where an optimum compromise between and is found. A simple model is developed correlating the fundamental physical properties of the soft magnetic wires with the measured values of both components of the impedance, allowing the prediction of experimental GMI ratios and an easy visualization of the phenomenon.

The effective anisotropy of hard-soft magnetic nanostructures is analyzed using the concept of the exchange correlation length of both phases. The dependence of coercivity on volume fraction, fluctuation length, temperature, and magnetic properties of the components is derived from the degree of magnetic coupling, defined through an effective interphase exchange constant. Coercivity and remanence measurements carried out on devitrified FeZrBCu amorphous alloys point out the transition from an uncoupled to a coupled regime by increasing the temperature in a very diluted system, according to the predictions of the analysis.

We report on the magnetic properties and the crystallographic structure of the cobalt nanowire arrays as a function of their nanoscale dimensions. X-ray diffraction measurements show the appearance of an in-plane hcp-Co phase for nanowires with 50 nm diameter, suggesting a partial reorientation of the magnetocrystalline anisotropy axis along the membrane plane with increasing pore diameter. No significant changes in the magnetic behavior of the nanowire system are observed with decreasing temperature, indicating that the effective magnetoelastic anisotropy does not play a dominant role in the remagnetization processes of individual nanowires. An enhancement of the total magnetic anisotropy is found at room temperature with a decreasing nanowire diameter-to-length ratio ͑d / L͒, a result that is quantitatively analyzed on the basis of a simplified shape anisotropy model.