Classical analogy for the deflection of flux avalanches by a metallic layer

Sudden avalanches of magnetic flux bursting into a superconducting sample undergo deflections of their trajectories when encountering a conductive layer deposited on top of the superconductor. Remarkably, in some cases flux is totally excluded from the area covered by the conductive layer. We present a simple classical model that accounts for this behaviour and considers a magnetic monopole approaching a semi-infinite conductive plane. This model suggests that magnetic braking is an important mechanism responsible for avalanche deflection.Comment: 14 pages, 5 figure

Measurement of critical current flow and connectivity in systems of joined square superconducting plates

A method to measure the electrical connectivity between square superconducting plates joined by weak link interfaces is presented. It is based on observation of lines where the flow of critical current abruptly changes direction due to the presence of weak links, and the confinement created by the shape of the sample. The method is demonstrated using magneto-optical imaging (MOI) of systems consisting of up to 2 X 2 plates joined to form a larger square. Common features are found in the current flow patterns, which allow to measure the electrical connectivity between the plates by observing an angle between pairs of lines indicating where the current abruptly changes flow direction, so-called discontinuity, or d-lines. The samples used in this study are Nb films with weak links created by focused ion beam machining

Genomic variability of Pantoea ananatis in maize white spot lesions assessed by AFLP markers.

Measures to control maize white spot (MWS) caused by Pantoea ananatis are preferentially based on resistant cultivars. A lack of knowledge on the genetic variability of pathogens could interfere with the development and utilization of controlling strategies in this pathosystem. The main goals of this study were to investigate the genetic variability of 90 P. ananatis isolates from three different eco-geographical regions of Brazil by amplified fragment length polymorphism (AFLP), and to determine the presence of a universal P. ananatis plasmid in isolates from tropical Brazil. Analysis of genetic similarity by AFLP allowed us to categorize the 90 isolates into two groups. However, no correlation between the collecting sites and genetic groupings was observed. The polymorphism percentage found in P. ananatis ranged between 24.64 and 92.46%, and genetic diversity was calculated to be 0.07-0.09. The analysis of molecular variance showed that 99.18% of genetic variability was within the populations, providing evidence that evolutionary forces were acting on these populations. All P. ananatis isolates showed the P. ananatis universal plasmid (280 or 352 kb). This is the first report on the presence of a universal P. ananatis plasmid from MWS lesions in the tropical area

Spin texture on top of vortex avalanches in Nb/Al_2O_3/Co thin film heterostructures

We report on magneto-optical imaging, magnetization, Hall effect and magneto-resistance experiments in Nb/Al_2O_3/Co thin film heterostructures. The magnetic field is applied perpendicularly to the plane of the film and gives rise to abrupt flux penetration of dendritic form. A magnetization texture is imprinted in the Co layer in perfect coincidence with these ramifications. The spin domains that mimic the vortex dendrites are stable upon the field removal. Moreover, the imprinted spin structure remains visible up to room temperature. Complementary magnetization, Hall effect and magneto-resistance experiments were performed in a similar sample where electrical contacts were placed on the Co layer. In the region of the field - temperature diagram where flux instabilities are known to occur in Nb films, irregular jumps are observed in the magnetic hysteresis and large amplitude noise is detected in the magneto-resistance and Hall resistivity data when measured as a function of the field.Comment: 13 pages, 8 figure

Citologia comparativa do processo de infecção do conídio falcado e oval de Colletotrichum sublineola em cultivar de sorgo suscetível e resistente.

O modo de infecção primária de Colletotrichum sublineola, agente causal da antracnose em sorgo, ocorre através de conídios falcados produzidos terminalmente em conidióforos nos acérvulos. Um tipo secundário de conídio, o conídio oval, de menor tamanho e ontogenia distinta dos falcados é também produzido por este patógeno. O objetivo deste estudo foi comparar, por meio de microscopia de luz, o processo de infecção entre estes dois tipos de conídios, os ovais e falcados de C. sublineola, em cultivares de sorgo resistente e suscetível à antracnose. Folhas destacadas de 25 dias de idade da BR009 (suscetível) e SC283 (resistente) foram inoculadas com ambos os conídios do isolado patogênico 204.01 e o processo de infecção foi acompanhado por microscopia ótica de 2 a 168 h após a inoculação (AI). Ambos os conídios germinaram 2 h AI e transcorridas 4 h AI, independentemente da cultivar, apressórios arredondados com superfície lisa foram formados diretamente dos conídios falcados, enquanto que apressórios ligeiramente irregulares foram formados na ponta dos tubos germinativos emitidos pelos conídios ovais. Na cultivar suscetível, os apressórios foram formados em maior frequência pelos conídios falcados, enquanto que na cultivar resistente estas estruturas foram formadas em maior frequência pelos conídios ovais. Poros de penetração e hifas de infecção foram visualizados em todos os materiais inoculados com ambos os conídios. Sintomas da doença foram visualizados primeiramente no material inoculado com conídios falcados e foi superior na cultivar suscetível. Lesões com acérvulos contendo conídios falcados foram visualizadas em todos os tratamentos fechando assim o ciclo de infecção

The activity of laurel essential oil (crude and fractions) in the control of adult bovine ticks and larvae

Ectoparasites cause direct and indirect losses to farmers, affecting the production of meat and milk and increasing the production costs due to the acquisition of acaricides to maintain cattle health. The financial losses caused by Rhipicephalus (Boophilus) microplus, which is the main livestock ectoparasite in Brazil, reach approximately US$ 3 billion annually. The aim of this study was to evaluate the acaricidal effect of the crude essential oil (EO) and EO’s fractions (FR) obtained from Laurus nobilis L. (Lauraceae) leaves on Rhipicephalus (Boophilus) microplus. Eight fractions were obtained, wherein five major compounds were identified (sabinene, α-terpinyl acetate, 1,8-cineole, linalool, and α-terpineol). The acaricidal activity of these FR was tested by the larval packet test. The EO was tested by the adult immersion test, and, at concentrations of 200, 100 and 50 µL/mL, the oil caused mortality of engorged females, egg mass reduction, and hatching inhibition. The fractions with α-terpineol and sabinene, as the major compounds, were the most active larvicides (LC50=0.13 µL/mL, LC99=0.51 µL/mL; and LC50=0.20 µL/mL, LC99=0.56 µL/mL, respectively). This assessment also indicated that fractionation was important since most of the fractions obtained were more active than the EO. Furthermore, this is the first report of laurel EO and its fractions employed in the control of cattle ticks. Thereby, new prospects for the use of this essential oil or its chromatographic fractions in products applied for cattle tick control can be opened up. However, studies in other stages of development of cattle ticks for the active fractions, and studies under field conditions, the effect on non-target organisms and residual effect on the environment are still needed to evaluate the acaricidal activity of EO and its active fractions