Particles-vortex interactions and flow visualization in He4

Recent experiments have demonstrated a remarkable progress in implementing and use of the Particle Image Velocimetry (PIV) and particle tracking techniques for the study of turbulence in He4. However, an interpretation of the experimental data in the superfluid phase requires understanding how the motion of tracer particles is affected by the two components, the viscous normal fluid and the inviscid superfluid. Of a particular importance is the problem of particle interactions with quantized vortex lines which may not only strongly affect the particle motion, but, under certain conditions, may even trap particles on quantized vortex cores. The article reviews recent theoretical, numerical, and experimental results in this rapidly developing area of research, putting critically together recent results, and solving apparent inconsistencies. Also discussed is a closely related technique of detection of quantized vortices negative ion bubbles in He4.Comment: To appear in the J Low Temperature Physic

Quantum turbulence in 4He, oscillating grids, and where do we go next?

Experimental approaches to the study of quantum turbulence (QT) in superfluid 4He in the low temperature limit, where the normal fluid density is effectively zero, are considered. A succinct general introduction covers liquid 4He, superfluidity, critical velocities for the onset of dissipation, quantized vortex lines and QT. The QT can be created mechanically by the oscillation of wires or grids above characteristic critical velocities. The interesting dynamics of the oscillating grid are discussed. It exhibits an enhanced effective mass due to backflow, as expected from classical hydrodynamics. It is found that the critical velocity attributable to the onset of QT production rises with increasing temperature. Oscillating objects like grids or wires create QT that is not well-characterized in terms of length scale, and the QT is not spatially homogeneous. The QT can be detected by the trapping of negative ions on vortex cores. Although the corresponding capture cross-section has not yet been measured, it is evidently very small, so that the technique cannot be expected to be a very sensitive one. In the future it is hoped to create well-characterized, homogeneous QT by means of a drawn grid. Improved sensitivity in the detection of QT is being sought through calorimetric techniques that monitor the temperature rise of the liquid caused by the decay of the vortex lines

Toler\ue2ncia de Himatanthus sucuuba Wood. (Apocynaceae) ao alagamento na Amaz\uf4nia Central

Himatanthus sucuuba is a tree species with known phytotherapic value which colonizes both white-water floodplains (várzea) and upland forests (terra firme) in Central Amazonian. The objective of this study was to compare germination and initial seedling development from seeds collected in both the ecosystems. There was no significant difference between dry seed mass, but in a four month period in a glasshouse in Manaus, Brazil, germination rate differed according to the substrate and origin of the seeds. In the substrate sand + sawdust (non-flooded) germination rate was high, independent of seed origin (várzea 94% and terra firme 91%). In the substrate constituted only by water (flooded), the seeds originating from várzea had a higher germination rate (96%) and seedling formation (84%) than those originating from terra firme which had a germination rate of 64% and none of the seeds formed seedlings. In this treatment, the radicles rot few days after their emission, indicating that the seeds originating from várzea present adaptive characteristics to the floodplain environment which are not present in seeds from terra firme

Substrato, temperatura de germinação e desenvolvimento pós-seminal de sementes de Dalbergia nigra Germination substrate, temperature and post-seminal development of Dalbergia nigra seeds

O objetivo deste trabalho foi definir o tipo de substrato e a temperatura mais adequada à germinação de sementes de Dalbergia nigra (Vell.) Fr. All. Ex Benth (jacarandá-da-bahia), e conhecer a morfologia de seu desenvolvimento pós-seminal e caracterizar as plântulas normais, o tipo de germinação e os padrões de anormalidade. As sementes foram semeadas nos substratos sobre papel, rolo de papel e sobre vermiculita, nas temperaturas constantes de 20, 25, 30 e 35&deg;C e alternadas de 20-30&deg;C e 20-35&deg;C. O delineamento estatístico empregado foi o inteiramente casualizado (6x3), com quatro repetições de 50 sementes. Foram analisados os seguintes parâmetros: porcentagem de germinação normal (plântulas normais) e velocidade de emergência de plântulas. Os melhores resultados foram verificados nas temperaturas de 25&deg;C e 20-30&deg;C, nos substratos sobre vermiculita e rolo de papel. Plântulas normais foram caracterizadas como faneroepígeas em relação ao tipo de germinação.<br>The objective of this work was to define the germination substrate of Dalbergia nigra (Vell.) Fr. All. Ex Benth (jacarandá-da-bahia), to evaluate the most appropriate temperature for its seeds germination, and to study its post-seminal morphology, showing normal and abnormal seedlings patterns. Seeds were sowed on filter paper, towel paper and vermiculite, using the constant temperatures of 20, 25, 30 and 35&deg;C as well as alternate temperatures of 20-30&deg;C and 20-35&deg;C. The statistical design was completely randomized (6x3) with 50 seeds sowed in four replications in which the following parameters were analyzed: normal germination (normal seedlings) percentage and speed emergence index. The best results were obtained for temperatures of 25&deg;C and 20-30&deg;C in vermiculite and towel paper substrates. Normal seedlings were classified as faneroepigeal germination type