7,134 research outputs found
Gas levitator having fixed levitation node for containerless processing
A method and apparatus is disclosed for levitating a specimen of material in a containerless environment at a stable nodal position independent of gravity. An elongated levitation tube has a contoured interior in the form of convergent section, constriction, and a divergent section in which the levitation node is created. A gas flow control means prevents separation of flow from the interior walls in the region of a specimen. The apparatus provides for levitating and heating the specimen simultaneously by combustion of a suitable gas mixture combined with an inert gas
Chaotic itinerancy and power-law residence time distribution in stochastic dynamical system
To study a chaotic itinerant motion among varieties of ordered states, we
propose a stochastic model based on the mechanism of chaotic itinerancy. The
model consists of a random walk on a half-line, and a Markov chain with a
transition probability matrix. To investigate the stability of attractor ruins
in the model, we analyze the residence time distribution of orbits at attractor
ruins. We show that the residence time distribution averaged by all attractor
ruins is given by the superposition of (truncated) power-law distributions, if
a basin of attraction for each attractor ruin has zero measure. To make sure of
this result, we carry out a computer simulation for models showing chaotic
itinerancy. We also discuss the fact that chaotic itinerancy does not occur in
coupled Milnor attractor systems if the transition probability among attractor
ruins can be represented as a Markov chain.Comment: 6 pages, 10 figure
Preliminary characterization of a one-axis acoustic system
The acoustic fields and levitation forces produced along the axis of a single-axis resonance system were measured. The system consisted of a St. Clair generator and a planar reflector. The levitation force was measured for bodies of various sizes and geometries (i.e., spheres, cylinders, and discs). The force was found to be roughly proportional to the volume of the body until the characteristic body radius reaches approximately 2/k (k = wave number). The acoustic pressures along the axis were modeled using Huygens principle and a method of imaging to approximate multiple reflections. The modeled pressures were found to be in reasonable agreement with those measured with a calibrated microphone
Method and apparatus for shaping and enhancing acoustical levitation forces
A method and apparatus for enhancing and shaping acoustical levitation forces in a single-axis acoustic resonance system wherein specially shaped drivers and reflectors are utilized to enhance to levitation force and better contain fluid substance by means of field shaping is described
Revision of the Antarctic and sub-Antarctic species of the family Stegocephalidae (Crustacea: Amphipoda) with description of two new species
The Antarctic and sub-Antarctic elements of the family Stegocephalidae DANA, 1855 (Crustacea: Amphipoda) are revised, and a key to the species is presented. Two new species are described: Andaniexis ollii n.sp. and Phippsiella watlingi n.sp. The family is represented in the Southern Ocean by 19 species belonging to 11 genera, of which one is reported as new to the area
Ultrafast spatio-temporal dynamics of terahertz generation by ionizing two-color femtosecond pulses in gases
We present a combined theoretical and experimental study of spatio-temporal
propagation effects in terahertz (THz) generation in gases using two-color
ionizing laser pulses. The observed strong broadening of the THz spectra with
increasing gas pressure reveals the prominent role of spatio-temporal reshaping
and of a plasma-induced blue-shift of the pump pulses in the generation
process. Results obtained from (3+1)-dimensional simulations are in good
agreement with experimental findings and clarify the mechanisms responsible for
THz emission
A carbonate-banded iron formation transition in the Early Protorezoicum of South Africa
Seven new and two resurveyed stratigraphic sections through the important carbonate-BIF transition in Griqualand West are presented and compared with six published sections. Lateral correlation within this zone is attempted but the variability was found to be too great for meaningful subdivision. Substantial lithological irregularity is the only unifying character of this zone, for which the new name Finsch Member (Formation) is proposed. Vertical and lateral lithological variations as well as chemical changes across this zone are discussed with reference to environmental aspects. Local and regional considerations lead to the conclusion that fresh water-sea water mixing occurred in a shallowing basin
Vergelijking N-bemestingsadviezen en N-wetgeving tussen een aantal EU-landen
Studie naar de verschillen en overeenkomsten tussen bemestingsadviezen en N-wetgeving tussen een aantal landen. De studie beperkte zich tot Vlaanderen (VL), Denemarken (DK), Duitsland (DL) en Frankrijk (FR) en tot de grote akkerbouwgewassen in Nederland (NL
Informatieblad Mineralen en Milieukwaliteit : perspectieven differentiatie N-bemestingsadviezen
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