Temperature dependence of the coercive field in single-domain particle systems

The magnetic properties of Cu97Co3 and Cu90Co10 granular alloys were measured over a wide temperature range (2 to 300K). The measurements show an unusual temperature dependence of the coercive field. A generalized model is proposed and explains well the experimental behavior over a wide temperature range. The coexistence of blocked and unblocked particles for a given temperature rises difficulties that are solved here by introducing a temperature dependent blocking temperature. An empirical factor gamma arise from the model and is directly related to the particle interactions. The proposed generalized model describes well the experimental results and can be applied to other single-domain particle system.Comment: 7 pages, 8 figures, revised version, accepted to Physical Review B on 29/04/200

Bistability, softening, and quenching of magnetic moments in Ni-filled carbon nanotubes

The authors apply first-principles calculations to investigate the interplay between structural, electronic, and magnetic properties of nanostructures composed of narrow nanotubes filled with metallic nanowires. The focus is on the structural and magnetic responses of Ni-filled nanotubes upon radial compression. Interestingly, metastable flattened structures are identified, in which radially deformed nanotubes are stabilized by the interactions with the encapsulated wire. Moreover, our results indicate a quenching of the magnetic moment of the wire upon compression, as a result of the transfer of charge from the $s$ to the $d$ orbitals of the atoms in the wire.Comment: 4 pages, 4 figure

Metodologia para elaboração de escalas diagramáticas para avaliação de doenças em planta.

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Desenvolvimento de Physocleora dimidiaria (Guenée, 1852) (Lepidoptera:Geometridae) em hospedeiros naturais.

Foi estudado o desenvolvimento de Physocleora dimidiaria (Guenée, 1852) em Malus domestica (MD), Trifolium repens (TR) e Rumex obtusifolius (RO) em laboratório. A duração da fase larval foi maior em MD (34,5 ± 0,89 dias) e menor em TR (23,4 ± 0,41 dias) e RO (24,9 ± 0,44 dias). O desenvolvimento de pupa (13 dias), peso de pupas (0,07g), fecundidade (entre 191,9 e 431 ovos), incubação (9 dias), longevidade (11 dias), pré-oviposição (1 dias), oviposição (7 dias) e a taxa líquida de reprodução (entre 59,3 e 183,6 fêmeas) não diferiram. A fertilidade foi menor em TR (20,5 ± 9,01 %) que em RO (71,5 ± 16,30 %). O tempo de uma geração foi superior em MD (60,0 ± 1,16 dias)

Seasonal susceptibility of apple trees to Neonectria ditissima wound infections.

European canker, caused by Neonectria ditissima, is an important disease of apple in the temperate climate of southern Brazil. Monthly inoculations of this fungus were carried out on various wound types on cvs ‘Gala’ and ‘Fuji’ over two productive cycles to better understand the seasonal susceptibility of apple trees. Wound types were: bud scars (September), petal scars (October), fruit-thinning scars (November), leaf scars (from November to May), fruit-picking wound scars for ‘Gala’ (February) and ‘Fuji’ (March), and pruning wounds (June to August). One hundred plants of each cultivar were used and inoculation sites were monitored periodically for symptom expression. At each assessment, visible lesions were counted and pruned, and wounds were painted. Differences in wound susceptibility occurred throughout the year. Most lesions resulted from inoculations of pruning wounds. Inoculations performed in spring on bud and petal scars resulted in lower disease expression than inoculations later in the season. Keywords European canker, Malus domestica, Nectria galligena, Neonectria ditissima, apple, wound