Effect of gas phase modification of analcime zeolite composite membrane on separation of surfactant by ultrafiltration

Ceramic–analcime zeolite composite membranes have been synthesized by hydrothermal crystallization of zeolite over clay supports. The zeolite layer is characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis and pore size distribution determined using the bubble point technique. The XRD pattern of the zeolite is found to match with JCPDS file #19-1180 which is an analcime-o zeolite of molecular formula NaAlSi₂O₆·H₂O having orthorhombic crystal structure with lattice parameters: a=13.72 Å, b=13.714 Å and c=13.714 Å. In this paper, we report a gas phase nitration scheme, in which we show through the elemental analysis that the modification of entire matrix (and not limited to pores and channels) occurs. The nitrated zeolite was reduced to aminated zeolite membrane by reacting it hydrazine hydrate.

Separation of surfactant (CPC) was performed using these three types (unmodified, nitrated and aminated) of membranes and it showed about 300% increase in the retention of the surfactant after its modification. Its hydrophilic nature also increases as shown by the increase in the permeate flux. In order to find the reason for this enhanced performance, structural analysis of the modified membranes was carried out. The XRD patterns of these were found to be identical and they did not match with those of any of the compounds given in the JCPDS files. The patterns were therefore indexed, using first principle, to find their crystal structure and it was found that the structure changed from orthorhombic for unmodified to tetragonal geometry for the modified zeolites. This also caused about 10% increase in the unit cell volume of the modified zeolites. Anion exchange capacity and the elemental analysis showed that the nitration occurred over the entire zeolite matrix (not restricted to the pores and channels) and on an average about one amine group was present in every second formula unit of the zeolite. This extensive presence of nitrate or amine group in the zeolite matrix makes the modified zeolite membrane highly hydrophilic and may be responsible for the increase in the retention of the surfactant and permeate flux for the modified membranes.     

BPS Quivers and Spectra of Complete {\mathcal{N} = 2} Quantum Field Theories

We study the BPS spectra of ${\mathcal{N}=2}$ N = 2 complete quantum field theories in four dimensions. For examples that can be described by a pair of M5 branes on a punctured Riemann surface we explain how triangulations of the surface fix a BPS quiver and superpotential for the theory. The BPS spectrum can then be determined by solving the quantum mechanics problem encoded by the quiver. By analyzing the structure of this quantum mechanics we show that all asymptotically free examples, Argyres-Douglas models, and theories defined by punctured spheres and tori have a chamber with finitely many BPS states. In all such cases we determine the spectrum.     

Brachistochrones in potential flow and the connection to Darwin's theorem

We establish the existence and the asymptotic properties of a path of minimum travel time for a line of particles starting upstream of a sphere or cylinder in potential flow. A connection is made between this brachistochrone path and Darwin's proposition which relates the added mass with the drift volume dragged by a body moving an infinite distance in the fluid. We compute an asymptotic correction to the drift volume for finite distances and show how the brachistochrone path is connected to the reflux volume. We present accurate numerical calculations for the brachistochrone position, point of zero horizontal Lagrangian displacement, reflux and partial drift volumes. These calculations are seen to agree well with the asymptotic predictions even for moderate values of the parameters. In the small Reynolds number regimes, we show that while for the case of Stokes flow past a sphere no brachistochrones exist at finite distances from the sphere, the Oseen correction is sufficient to restore such least-time trajectories. Lastly, the application to a sphere falling in a stratified fluid is discussed using the new drift volume correction formula.     

Designing tubular conducting polymer actuators for wireless electropumping

Rational design and shaping of soft smart materials offer potential applications that cannot be addressed with rigid systems. In particular, electroresponsive elastic materials are well-suited for developing original active devices, such as pumps and actuators. However, applying the electric stimulus requires usually a physical connection between the active part and a power supply. Here we report about the design of an electromechanical system based on conducting polymers, enabling the actuation of a wireless microfluidic pump. Using the electric field-induced asymmetric polarization of miniaturized polypyrrole tubes, it is possible to trigger simultaneously site-specific chemical reactions, leading to shrinking and swelling in aqueous solution without any physical connection to a power source. The complementary electrochemical reactions occurring at the opposite extremities of the tube result in a differential change of its diameter. In turn, this electromechanical deformation allows inducing highly controlled fluid dynamics. The performance of such a remotely triggered electrochemically active soft pump can be fine-tuned by optimizing the wall thickness, length and inner diameter of the material. The efficient and fast actuation of the polymer pump opens up new opportunities for actuators in the field of fluidic or microfluidic devices, such as controlled drug release, artificial organs and bioinspired actuators.

Tubular conducting polymer actuators are used for developing a wireless electropumping device. Bipolar electrochemistry, allowing symmetry breaking in terms of polarization and electrochemical reactions, is the key ingredient for efficient pumping.     

Bifurcation to heteroclinic cycles and sensitivity in three and four coupled phase oscillators

We study the bifurcation and dynamical behaviour of the system of N globally coupled identical phase oscillators introduced by Hansel, Mato and Meunier, in the cases N=3 and N=4. This model has been found to exhibit robust ‘slow switching’ oscillations that are caused by the presence of robust heteroclinic attractors. This paper presents a bifurcation analysis of the system in an attempt to better understand the creation of such attractors. We consider bifurcations that occur in a system of identical oscillators on varying the parameters in the coupling function. These bifurcations preserve the permutation symmetry of the system. We then investigate the implications of these bifurcations for the sensitivity to detuning (i.e. the size of the smallest perturbations that give rise to loss of frequency locking).For N=3 we find three types of heteroclinic bifurcation that are codimension-one with symmetry. On varying two parameters in the coupling function we find three curves giving (a) an S₃-transcritical homoclinic bifurcation, (b) a saddle-node/heteroclinic bifurcation and (c) a Z₃-heteroclinic bifurcation. We also identify several global bifurcations with symmetry that organize the bifurcation diagram; these are codimension-two with symmetry.For N=4 oscillators we determine many (but not all) codimension-one bifurcations with symmetry, including those that lead to a robust heteroclinic cycle. A robust heteroclinic cycle is stable in an open region of parameter space and unstable in another open region. Furthermore, we verify that there is a subregion where the heteroclinic cycle is the only attractor of the system, while for other parts of the phase plane it can coexist with stable limit cycles. We finish with a discussion of bifurcations that appear for this coupling function and general N, as well as for more general coupling functions.     

Dynamics of a nonlinear microresonator based on resonantly interacting flexural-torsional modes

A novel microresonator operating on the principle of nonlinear modal interactions due to autoparametric 1:2 internal resonance is introduced. Specifically, an electrostatically actuated pedal-microresonator design, utilizing internal resonance between an out-of-plane torsional mode and a flexural in-plane vibrating mode is considered. The two modes have their natural frequencies in 1:2 ratio, and the design ensures that the higher frequency flexural mode excites the lower frequency torsional mode in an autoparametric way. A Lagrangian formulation is used to develop the dynamic model of the system. The dynamics of the system is modeled by a two degrees of freedom reduced-order model that retains the essential quadratic inertial nonlinearities coupling the two modes. Retention of higher-order model for electrostatic forces allows for the study of static equilibrium positions and static pull-in phenomenon as a function of the bias voltages. Then for the case when the higher frequency flexural mode is resonantly actuated by a harmonically varying AC voltage, a comprehensive study of the response of the microresonator is presented and the effects of damping, and mass and structural perturbations from nominal design specifications are considered. Results show that for excitation levels above a threshold, the torsional mode is activated and it oscillates at half the frequency of excitation. This unique feature of the microresonator makes it an excellent candidate for a filter as well as a mixer in RF MEMS devices.     

Some recent advances in the theory of homogeneous isotropic turbulence

We review some advances in the theory of homogeneous, isotropic turbulence. Our emphasis is on the new insights that have been gained from recent numerical studies of the three-dimensional Navier Stokes equation and simpler shell models for turbulence. In particular, we examine the status of multiscaling corrections to Kolmogorov scaling, extended self similarity, generalized extended self similarity, and non-Gaussian probability distributions for velocity differences and related quantities. We recount our recent proposal of a wave-vector-space version of generalized extended self similarity and show how it allows us to explore an intriguing and apparently universal crossover from inertial- to dissipation-range asymptotics.     

Mononuclear and long-range single-bridged binuclear complexes of oxovanadium(IV) involving conjugated heterocyclic nitrogen base and heterocyclic β-diketones

Summary Binuclear complexes of OV^IV have been prepared by reacting aromatic diamines with mixed-ligand (mononuclear) complexes of the type [(diamine), VO(PmAcp or PmbzP)], where (diamine) = 2,2-bipyridine or 1,10-phenanthroline, and PmAcp or PmbzP heterocyclic -diketone ligands = 1-phenyl-3-methyl-4-acetyl or 4-benzoyl-2-pyrazolin-5-one. 2,6-Diaminopyridine orm-phenylenediamine condenses with the MeCO or PhCO groups of PmAcp and PmbzP on two complex molecules, thus bridging the two VO^II centres. The complexes have been characterized by electronic, i.r. and e.s.r. spectra, magnetic measurements, thermogravimetry, conductometry and microanalysis. The magnetic moments and the order of antiferromagnetism are explained on the basis of delocalized -orbitals, orientation of the metal orbitals and the bridging Schiff base. The metal-ligand bond is covalent.