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The mechanism of coke formation on silica-alumina cracking catalysts was studied by analysis of cracking experiments with seven pure hydrocarbons at 445' C. and n-hexadecane at 500" C. under a variety of process conditions. Coke deposits were isolated from selected catalyst samples for infrared spectral examination. Aromatic skeletal vibrations were observed a t 1580 to 1590 cm.-' Although the cokes were low in hydrogen content, it was possible to identify -Ctlz, -CH3, and aromatic -CH groups by infrared absorption in the C-H stretch region. Mechanism of coke formation involves initial adsorption of hydrocarbons followed by chemical reactions of adsorbed materials. The latter include condensation reactions followed b y hydrogen elimination either by direct dehydrogenation to form hydrogen gas or by a hydrogen transfer process. Coke formation in fixed beds is shown to b e a complex function of length of

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We report on a fluidic resonant waveguide grating (RWG) biosensor system that enables medium throughput measurements of cellular responses under microfluidics in a 32-well format. Dynamic mass redistribution assays under microfluidics differentiate the cross-desensitization process between the β2-adrenoceptor agonist epinephrine and the adenylate cyclase activator forskolin mediated signaling. This system opens new possibility to study cellular processes that are otherwise difficult to achieve using conventional RWG configurations.

The properties of physical systems whose observable properties depend upon random exceedances of critical parameters are quantitatively examined. Using extreme value theory, the dynamical behavior of this broad class of systems is derived. This class of systems can exhibit two characteristic signatures: generalized activation when far from equilibrium and noise with a characteristic power spectrum (including 1/f ) when in quasiequilibrium. Fractal structures can also arise from these systems. It is thus demonstrated that generalized activation, noise, and fractals, in some cases, are simply different manifestations of a single common dynamical principle, which is termed ‘‘extremal dynamics.’’ Examples of physical processes governed by extremal dynamics are discussed, including data loss of nonvolatile memories and dielectric breakdown.