Ligament-mediated spray formation

The spray formed when a fast gas stream blows over a liquid volume presents a wide distribution of fragment sizes. The process involves a succession of changes of the liquid topology, the last being the elongation and capillary breakup of ligaments torn off from the liquid surface. The coalescence of the liquid volumes constitutive of a ligament at the very moment it detaches from the liquid bulk produces larger drops. This aggregation process has its counterpart on the shape of the size distribution associated with the ligament breakup, found to be very well represented by gamma distributions. The exponential shape of the overall distribution in the spray coincides with the large excursion wing of these elementary distributions, underlying the crucial role played by the ligament dynamics in building up the broad statistics of sprays

Upscaling Flow and Transport Processes

Peer reviewe

The impact of the Euro on securities markets

No Abstract. Securities Market Journal Vol. 10 (2) 2005: pp. 42-4

Persistency of material element deformation in isotropic flows and growth rate of lines and surfaces

We explore the consequence of isotropy on the growth of material lines and surfaces in complex flows. We show that the key parameter is the persistency $\gamma \tau$, defined as the product of a typical stretching rate γ to its associated coherence time τ. In particular, we derive the dependence of the net growth rate of both lines and surfaces on $\gamma \tau$. Their growth rates increase strongly with increasing persistencies for small $\gamma \tau$, and then saturate for $\gamma \tau \geq 10$. Making use of measurements of Girimaji and Pope [1], we estimate the persistency $\gamma \tau$ to be of order 1 in isotropic turbulence. We then comment on the evolution of the shape of an initially spherical material blob. While its length increases, one of its tranverse dimension increases slowly and the other one decreases. This quasi-two-dimensional deformation leads a final ribbon-shape

On the bubble shape in a magnetically compensated gravity environment

International audienceWe investigate the shape of bubbles in liquid oxygen under magnetic levitation conditions: a magnetic field is applied that polarizes bulk oxygen, and its spatial variation induces a body force opposed to its weight. In these conditions, bubbles appear to have a smooth ellipsoidal shape, which may be prolate (elongated in the vertical direction), oblate (elongated in the horizontal plane) or perfectly spherical. The dependence of the elongation ratio η on the volume and levitation position is explored. It is found that the bubble shape is prescribed by the minimization of the sum of surface tension, demagnetization and magnetic–gravitational potential energies

On two-dimensional foam ageing

International audienceThe present study aims at documenting, making use of an original set-up allowing to acquire well-converged data, the coarsening of foams in two dimensions. Experiments show that a foam behaves quite differently depending on the way it has been prepared. We distinguish between an initially quasi-monodisperse foam and a polydisperse foam. The coarsening laws are initially different, although both foams reach a common, time-dependent asymptotic regime. The ageing process relies on exchanges between adjacent foam cells (von Neumann's law), and on topological rearrangement (T(1) and T(2) processes) whose rates are measured in all regimes. We attempt to make their contribution to the evolution of the area S and facet number n distribution of probability P(S, n, t) quantitative. The corresponding mean field theory predictions represent well the phenomenon qualitatively, and are sometimes in quantitative agreement with the measurements. A simplified version of this theory, taking the form of a Langevin model, explains in a straightforward manner the different scaling laws in the different regimes, for the different foams

Renegotiation of joint venture contracts: The influence of boards of directors and prior ties as alternative governance mechanisms

Research on alliance governance has pointed out that joint ventures (JVs) are particularly complex forms of collaboration. Partnering firms therefore often face difficulties in anticipating contingencies and collaborative behaviors at the contract negotiation stage. When initial JV contracts are incomplete, renegotiation represents a key strategic opportunity for enhancing contractual safeguards or coordination guidelines over the course of the joint venture. Costs and risks entailed by renegotiating JV arrangements at a later stage are far from trivial, however. Existing research on alliances suggests that practitioners have alternative relational and formal governance solutions at their disposal for handling possible inefficiencies caused by contractual gaps over time. Although insightful, this research does not enable a determination as to whether these alternative relational and formal mechanisms substitute for or facilitate ex post contractual renegotiation. The competing arguments found in the literature provide little guidance to JV practitioners as well. Our results show that the collaborative context within which the JV is embedded (i.e., prior inter-partner ties) obviates the need for enhancing incomplete JV contracts ex post. By contrast, ex post contractual adjustments are fostered and facilitated by the formal and administrative apparatus engaged over the course of the JV (i.e., an involved JV board of directors). Such opposing effects suggest that prior ties can “prevent” the occurrence of inefficiencies caused by contractual gaps, while an involved JV board primarily can act as a mediation and renegotiation platform to “repair” the exchange when inefficiencies occur. Our findings highlight the multidimensional nature of joint venture governance, and in particular the interplay among various formal and informal governance solutions in the execution of joint ventures. By unpacking their complex effects on the decision to renegotiate incomplete JV contracts, our study also holds important value for managers seeking to govern their JVs over time

Aislamiento y purificación del virus X de la papa y clonación del gen de su cubierta proteica

In this work we describe the construction of potato virus X coat protein (PVX-CP) gene clones from a Colombian isolate. Virus was isolated from field potato plants cultured at páramo de San Jorge. PVX particles were purified from Nicotiana tabacum leaves infected with a local lesion taken from Datura stramonium plants. The genomic RNA present in the virus particles consisted of a single species of about 6 Kb. cDNA synthesis representing genomic RNA was followed by Digoxigenin incorporation after priming with oligonucleotide 4DT/KPN. PCR amplification of CP gene sequence was made by using oligonucleotides OX6 and L/Kpn. An expected fragment of 870 bp, besides some 600-123 bp fragments, was obtained after PCR. The blunt-ended fragments were clonned into the PCR cloning pMOSblue plasmid. The insert size of the selected recombinant cDNA clones was determined by restriction analysis of the plasmidDNAwith Sma I and Hind III enzymes. Positive clones were also screened by direct colony PCR screening. The selected recombinant cDNA clones were stored in glycerol at .70 °C.El objetivo principal de este trabajo fue obtener clones del gen que codifica la cubierta proteica (CP) del virus X de la papa (PVX). Para lograrlo se estudió un aislamiento colombiano del PVX obtenido de muestras de plantas de papa recolectadas en el páramo de San Jorge (CORPOICA). Después de la inoculación sobre Datura stramonium, se tomó una lesión local producida sobre este hospedero y se inocul ó sobre Nicotiana tabacum, de cuyo tejido se purificó el PVX. El RNA genómico extraído de las partículas virales purificadas presentó un tamaño de aproximadamente 6 Kb. La síntesis del cDNA, utilizando el primer 4DT/KPN, se evidenció mediante la incorporación de Digoxigenina. La amplificación por PCR del gen CP, a partir del cDNA sintetizado, se realizó utilizando el primer OX6 junto con el primer LK/pn, complementario a la secuencia del extremo 5´ del primer 4DT/KPN. El producto de la amplificación presentó el tamaño esperado de aproximadamente 870 pb, en adición a otros productos de 600-123 pb. Estos fragmentos amplificados fueron clonados en el plásmido pMOSBlue. Los recombinantes fueron analizados en “minipreps”, digiriendo el plásmido con Sma I y Hind III o utilizando el método de amplificación con PCR directamente de la colonia. Las colonias transformadas con el inserto apropiado fueron almacenadas en glicerol a -70 °C

Aislamiento y purificación del virus X de la papa y clonación del gen de su cubierta proteica

El objetivo principal de este trabajo fue obtener clones del gen que codifica la cubierta proteica (CP) del virus X de la papa (PVX). Para lograrlo se estudió un aislamiento colombiano del PVX obtenido de muestras de plantas de papa recolectadas en el páramo de San Jorge (CORPOICA). Después de la inoculación sobre Datura stramonium, se tomó una lesión local producida sobre este hospedero y se inocul ó sobre Nicotiana tabacum, de cuyo tejido se purificó el PVX. El RNA genómico extraído de las partículas virales purificadas presentó un tamaño de aproximadamente 6 Kb. La síntesis del cDNA, utilizando el primer 4DT/KPN, se evidenció mediante la incorporación de Digoxigenina. La amplificación por PCR del gen CP, a partir del cDNA sintetizado, se realizó utilizando el primer OX6 junto con el primer LK/pn, complementario a la secuencia del extremo 5´ del primer 4DT/KPN. El producto de la amplificación presentó el tamaño esperado de aproximadamente 870 pb, en adición a otros productos de 600-123 pb. Estos fragmentos amplificados fueron clonados en el plásmido pMOSBlue. Los recombinantes fueron analizados en “minipreps”, digiriendo el plásmido con Sma I y Hind III o utilizando el método de amplificación con PCR directamente de la colonia. Las colonias transformadas con el inserto apropiado fueron almacenadas en glicerol a -70 °C

3D reconstruction of dynamic liquid film shape by optical grid deflection method

In this paper, we describe the optical grid deflection method used to reconstruct the 3D profile of liquid films deposited by a receding liquid meniscus. This technique uses the refractive properties of the film surface and is suitable for liquid thickness from several microns to millimeter. This method works well for strong interface slopes and changing in time film shape; it applies when the substrate and fluid media are transparent. The refraction is assumed to be locally unidirectional. The method is particularly appropriate to follow the evolution of parameters such as dynamic contact angle, triple liquid-gas-solid contact line velocity or dewetting ridge thickness