The study of weak oscillatory flows in space experiments

The effects of residual accelerations have been studied by using three-dimensional modeling of the flow in a rectangular cell filled with a liquid, Pr=20, the walls of which were kept at different temperatures. The system was subjected to an acceleration field, which can be decomposed into two parts: a steady component and another one which varies slowly with time, the frequency is about f₀≈10⁻³ Hz. The convective heat transport and flow characteristics are discussed for different parameters of g-jitter. The high and low frequency modulation of a sinusoidal g-jitter is discussed. To capture many of the essential characteristics of buoyancy-induced convection a new approach is suggested, which was developed based on the observation of the trajectories of tracer particles. On the one hand, it is a typical way to record the flow in experiments. On the other hand, creating database of different types of trajectories gives the possibility to solve the inverse problem. The shape of the trajectory depends on the g-jitter parameters. It is shown that for slow convective motions the tracer particles perform loops along trajectory due to g-jitter with low frequencies, and the additional high frequencies only cause trembling of the shape of these loops. Taking the experimentally recorded trajectories of tracer particles and comparing with those in the database, one can draw a conclusion about the amplitude and direction of the resulting gravity vector during the experiment.     

Drying nano particles solution on an oscillating tip at an air liquid interface: what we can learn, what we can do

Evaporation of fluid at micro and nanometer scale may be used to self-assemble nanometre-sized particles in suspension. Evaporating process can be used to gently control flow in micro and nanofluidics, thus providing a potential mean to design a fine pattern onto a surface or to functionalize a nanoprobe tip. In this paper, we present an original experimental approach to explore this open and rather virgin domain. We use an oscillating tip at an air liquid interface with a controlled dipping depth of the tip within the range of the micrometer. Also, very small dipping depths of a few ten nanometers were achieved with multi walls carbon nanotubes glued at the tip apex. The liquid is an aqueous solution of functionalized nanoparticles diluted in water. Evaporation of water is the driving force determining the arrangement of nanoparticles on the tip. The results show various nanoparticles deposition patterns, from which the deposits can be classified in two categories. The type of deposit is shown to be strongly dependent on whether or not the triple line is pinned and of the peptide coating of the gold nanoparticle. In order to assess the classification, companion dynamical studies of nanomeniscus and related dissipation processes involved with thinning effects are presented.     

Microwave active resonator band-pass filters in various mmic technologies

In this article, two topologies of L-C parallel active resonators are presented. These circuits are realized in MMIC technology, using three transistors which could be MESFET, hemt or HBT. The survey of these resonators shows the possibility, by controling the values of a resistor and/or a capacitor, on the one hand, to tune the resonance frequency of these circuits, and on the other hand, to cancel out their losses so as to obtain negative conductance. Compact, lossless and narrow-band filters are then implemented using previous active resonators. To date, the use of mesfet technology has reduced the synthesis of such active filters in S-band and at X-band low frequencies. Now, however, hemt and HBT technologies allow the extension of their implementation to the whole X-band. This survey is illustrated by the simulated response of a 10 GHz filter with a 500 MHz 3 dB bandwidth. The mmic technology is a 0.2 μm hemt one. The simulated performances of this filter achieve a mean transmission gain of 0. 5 dB, with a reflection loss higher than 10 dB at 10 GHz,     

A Broadband CPW-to-Microstrip Modes Coupling Technique

A broadband vertical transition from coplanar waveguide (CPW)-to-microstrip modes is presented. The transition has a double resonance and can be tuned for very wide-band operation. The CPW-to-microstrip modes coupling technique is useful for the vertical integration of multi-layer millimeter-wave circuits, packaging and antenna feeding networks. A vertical transition has been fabricated on 100 μm silicon substrate for operation at W-band frequencies and shows less than 0.3 dB of insertion loss and better than 12 dB of return loss from 75 to 110 GHz. A 94 GHz CPW-fed microstrip antenna showing a 10-dB bandwidth of about 30 % has been built using the same transition technique.     

Stress-strain relationships in uniaxial extension of high cis-1,4-polyisoprene networks with different molecular weight precursors

Equilibrium stress-strain relationships in uniaxial extension for high cis-1,4-polyisoprene (Shell IR 307) networks were obtained by extrapolation of relaxation measurements to infinite time through a BKZ constitutive equation. Three series of networks were investigated, each series being characterized by its polymer precursor molecular weight. Influence of crosslinking density was studied through varying amounts of dicumyl peroxide as crosslinking agent. These results were used to test Flory and Erman's recent molecular elasticity theory of imperfect networks with constraints on junctions. It was shown that this later theory treating entanglements as restrictions on junction fluctuations could be reasonably used to characterize network topology. A universal value of 0.50 for the interpenetration parameter I is confirmed and an interpretation of parameter ζ in terms of network inhomogeneity is tentatively given.     

Monoepoxy polymerization initiated by BF3-amine complexes in bulk. III. Influence of γ-butyrolactone on polymer formation

The influence of γ-butyrolactone (γ-BL), used as solvent of BF₃-amine complexes, on the polymerization of monoepoxides was studied. Different intermediate reaction products of PGE initiated by BF₃-4-methoxyaniline (BF₃-4MA) previously solubilized in γ-BL (55% by weight), were separated and analyzed by ¹H-NMR. It is shown that there is the opening of both epoxy and γ-BL. The latter does not homopolymerize, but copolymerizes well with epoxy groups. The use of a large quantity of γ-BL leads to a decreasing molar mass of the formed polymer. The kinetic study allowed to propose the mechanism of the cationic polymerization of epoxy initiated by BF₃-amine complex in the presence of γ-BL. © 1994 John Wiley & Sons, Inc.     

Circulating fluidized bed combustion of pitches derived from heavy oil upgrading

Combustion trials were conducted with two pitch materials in the University of British Columbia pilot scale (152 mm × 152 mm × 7.3 m) circulating fluidized bed combustion unit. The pitches, which were bottom end by-products of heavy oil upgrading processes containing high concentrations of sulphur, heavy metals and asphaltenes, were fed to the combustor in liquid form and atomized in the combustion chamber. Limestone was fed also to capture sulphur in situ. The combustion efficiency was always above 99%. NO_x emissions increased as the Ca:S ratio increased. The heavy metal elements present in the pitch were found to remain essentially in the solid residue.     

Hardness and fracture toughness of thermoelectric La<Subscript>3−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript>4</Subscript>

Lanthanum telluride (La_3?x Te₄) is a state-of-the-art n-type high temperature thermoelectric material that behaves as a weak and brittle ceramic. Vickers microindentation hardness testing was explored as a rapid analysis technique to characterize the mechanical properties of this material. An indentation size effect was observed with hardness values ranging from 439 ± 31 kgf/mm² (0.01 kgf/10 s contact time) to 335 ± 6 kgf/mm² (0.5 kgf/10 s contact time). The Vickers indentation fracture toughness, K _VIF, based on measurements of crack lengths emanating from the corners of the Vickers indents was 0.70 ± 0.06 MPa m^1/2.