Continuous membrane oscillators

As indicated in section 1.3, cytosolic Ca oscillations, which occur in a variety of cell types as a result of stimulation by hormones or neurotransmitters, are among the most widespread of cellular rhythms, besides oscillations driven by periodic variations of the membrane potential in electrically excitable cells. These oscOlations, whose period varies from seconds to minutes depending on the cell type, sometimes occur spontaneously. Part V is devoted to this phenomenon, which clearly represents the most significant addition to the field of biochemical oscillations over the last decade, in addition to the evidence that has acciunulated to show that a continuous biochemical oscillator controls the eukaryotic cell cycle (see below). Experimental work on Ca oscillations has increased so much over the last years that it is by now the most studied biochemical rhythm. 

Two aqueous phases separated by a liquid membrane, EM, of nitrobenzene, NB, were layered in a glass tube, which was equipped with Pt counterelectrodes in W1 and W2 and reference electrodes in three phases as in Eq. (1). Reference electrodes set in W1 and W2 were Ag/AgCl electrodes, SSE, and those in LM were two tetraphenylborate ion selective electrodes [26,27], TPhBE, of liquid membrane type. The membrane current, /wi-w2 was applied using two Pt electrodes. The membrane potential, AFwi-wi recorded as the potential of SSE in W2 vs. that in W1. When a constant current of 25 /aA cm was applied from W1 to W2 in the cell given as Eq. (1), the oscillation of membrane potential was observed as shown in curve 1 of Fig. 1. The oscillation of AFwi-wi continued for 40 to 60 min, and finally settled at ca. —0.40 V. 

Though potential oscillation of the nitrobenzene membrane became more continuous and regular in contrast to the Dupeyrat-Nakache system, the establishment of a reproducible... 

Continuous Multicomponent Distillation Column 501 Gas Separation by Membrane Permeation 475 Transport of Heavy Metals in Water and Sediment 565 Residence Time Distribution Studies 381 Nitrification in a Fluidised Bed Reactor 547 Conversion of Nitrobenzene to Aniline 329 Non-Ideal Stirred-Tank Reactor 374 Oscillating Tank Reactor Behaviour 290 Oxidation Reaction in an Aerated Tank 250 Classic Streeter-Phelps Oxygen Sag Curves 569 Auto-Refrigerated Reactor 295 Batch Reactor of Luyben 253 Reversible Reaction with Temperature Effects 305 Reversible Reaction with Variable Heat Capacities 299 Reaction with Integrated Extraction of Inhibitory Product 280... 

Another technique is to assemble the particles under the influence of a liquid flow field, as achieved by filtering the dispersion. A membrane with pore sizes smaller than the particle diameter is used while continuously drawing the dispersion through a funnel, and the colloidal particles are retained at the membrane surface and accumulate [30,52]. Simultaneous application of an oscillating shear field during the filtration process improves the quality of particle ordering [53]. 

Introduction of membranes may, in some cases, lead to more flexibility in the design and study of chemical oscillators. The continuous-stirred tank reactor (CSTR) configuration, which is often used to study chemical oscillators because it maintains reaction and product concentrations away from equilibrium [1, 2], controls the transport of reactants, intermediates, and products by fluid flow, and does not discriminate among species. Membrane selectivity between chemical species can provide a basis for selection of dynamical behaviors that are unavailable with a CSTR. 

Chapter 6, Mechanically Driven Tunable Microlenses, continues with examples of microlenses tuned by a variety of mechanical methods. These mechanically tunable microlenses can be categorized as thin-membrane lenses with varying apertures, pressures, and surface shapes swellable hydrogel lenses liquid-liquid interface lenses actuafed by environmentally stimuli-respon-sive hydrogels and oscillating lens arrays driven by sound waves. 

There are oscillations in the shear stress on the membrane surface due to the continuous passing of bubbles near the membrane wall... 

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