Nonlinear instability of a viscous liquid jet

We investigate the weakly nonlinear temporal instability of an axisymmetric Newtonian liquid jet. Early nonlinear studies on the capillary instability of inviscid liquid jets were carried up to the third order contributions to the jet deformation and showed the nonlinear interaction between different modes. A recent study on the weakly nonlinear instability of planar Newtonian liquid sheets revealed the role of the liquid viscosity in the sheet stability behavior and showed a complicated influence [1]. Here, the instability of a liquid jet is examined as the axisymmetric counterpart of the sheet, in search for corresponding insight into the role of the liquid viscosity in the jet instability mechanism. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Analysis and validation of the phosphorylated metabolites of two anti-human immunodeficiency virus nucleotides (stavudine and didanosine) by pressure-assisted CE-ESI-MS/MS in cell extracts: sensitivity enhancement by the use of perfluorinated acids and alcohols as coaxial sheath-liquid make-up constituents

A CE method utilizing triple quadrupole electrospray (ES) MS (MS/MS) detection was developed and validated for the simultaneous measurement of nucleoside 5'-triphosphate and 5'-monophosphate anabolites of the anti-HIV (human immunodeficiency virus) didanosine (ddAMP, ddATP) and stavudine (d4TMP, d4TTP), among a pool of 14 endogenous 5'-mono-, di-, and triphosphate nucleosides. These compounds were spiked and extracted from peripheral blood mononuclear cells (PBMCs) which are the sites of HIV replication and drug action. An acetic acid/ammonia buffer (pH 10, ionic strength of 40 mM) was selected as running electrolyte, and the separation was performed by the simultaneous application of a CE voltage of +30 kV and an overimposed pressure of 28 mbar (0.4 psi). The application of pressure assistance was needed to provide stable ES conditions for successful coupling. The coupling was carried out with a modified sheath-flow interface, with one uninterrupted capillary (80 cmx 50 microm id; 192 microm od) in a dimension that fits into the ESI needle to get a stable ion spray. Some CE-MS parameters such as overimposed pressure, sheath-liquid composition, sheath-liquid and sheath-gas flow rates, ES voltage, and the CE capillary position were optimized in order to obtain an optimal sensitivity. The use of perfluorinated alcohols and acids in the coaxial sheath-liquid make-up (2,2,2-trifluoroethanol + 0.2 mM tridecafluoroheptanoic acid) appeared to provide the best MS sensitivity and improve the stability of spray. The linearity of the CE-MS and CE-MS/MS methods was checked under these conditions. Validation parameters such as accuracy, intraday and interday precision, and LOQs were determined in CE-MS/MS mode. Finally, the quantitation of d4T-TP and ddA-TP was validated in this CE-MS/MS system.     

Deforming static fluid interfaces with magnetic fields: application to the Rayleigh–Taylor instability

Shaping arbitrary fluid interfaces opens interesting perspectives for fluid-based processes and experiments. We demonstrate an experimental method to create non-planar static interfaces of almost arbitrary shape between two fluids, one of which is made highly magnetically permeable by the addition of a magnetic compound. By relying on spatially modulated magnetic fields, a non-homogeneous magnetic force is added to Earth's gravitational force, and a non-planar static interface can be stabilized. Precision experimental measurements are possible because we have developed a general method that allows us to predict numerically the shape of the interface, thereby facilitating the optimal experimental design before actually implementing it. As a first example, we apply this method to the Rayleigh–Taylor instability between two immiscible fluids. The results we obtain demonstrate the feasibility of the experimental method and the accuracy of the numerical predictions.