Experimental test of scaling of mixing by chaotic advection in droplets moving through microfluidic channels

This letter describes an experimental test of a simple argument that predicts the scaling of chaotic mixing in a droplet moving through a winding microfluidic channel. Previously, scaling arguments for chaotic mixing have been described for a flow that reduces striation length by stretching, folding, and reorienting the fluid in a manner similar to that of the baker's transformation. The experimentally observed flow patterns within droplets (or plugs) resembled the baker's transformation. Therefore, the ideas described in the literature could be applied to mixing in droplets to obtain the scaling argument for the dependence of the mixing time, t~(aw/U)log(Pe), where w [m] is the cross-sectional dimension of the microchannel, a is the dimensionless length of the plug measured relative to w, U [m s(-1)] is the flow velocity, Pe is the Péclet number (Pe=wU/D), and D [m(2)s(-1)] is the diffusion coefficient of the reagent being mixed. Experiments were performed to confirm the scaling argument by varying the parameters w, U, and D. Under favorable conditions, submillisecond mixing has been demonstrated in this system.     

Minimax hedging strategy

We present several variants of a robust risk management strategy based on minimax for the writer of a European call option on a stock and show that it performs at least as well as the standard hedging strategy, delta hedging. When using the minimax strategy, the hedger specifies a worst case scenario in terms of the price of the underlying stock. The minimax strategy recommends the number of shares in the underlying stock the hedger should hold in order to minimize the hedging error against the worst case occurring. The minimax hedging error may correspond to an extreme point of the price range being considered or to a mid-range solution. Simulation and empirical results suggest that the minimax strategy is particularly powerful for hedging the risk of writing an option when the price of the underlying stock is both highly volatile and crosses over the exercise frequently.     

Scanning tunneling microscopy study of porous carbon impregnated with palladium chloride

Mesoporous carbon Sibunit impregnated with aqueous solutions of H₂PdCl₄ has been studied with STM. The spontaneous reduction of Pd during the impregnation was confirmed by AES. The surface topography depends on the Pd surface coverage. When the Pd content on the surface is small, particles with an average diameter of ca. 2 nm are frequently observed, which are never imaged on the clean carbon support. When the Pd content is high, the surface still consists of small ca. 3–5 nm particles.     

Stochastic Optimization and Worst-Case Analysis in Monetary Policy Design

In this paper we compare expected loss minimization to worst-case or minimax analysis in the design of simple Taylor-style rules for monetary policy. To this end we use a small model estimated for the euro area by Orphanides and Wieland (2000). We find that rules optimized under a minimax objective in the presence of general parameter and shock uncertainty do not imply extreme policy activism. Such rules also tend to obey the Brainard principle, which implies that policy responsiveness declines with increasing uncertainty about policy effectiveness. We find that rules derived by means of minimax analysis are effective insurance policies limiting maximum loss over ranges of parameter values to be set by the policy maker. In practice, we propose to set these ranges with an eye towards the cost of such insurance cover in terms of the implied increase in expected inflation variability. JEL Classifications System: E52, E58, E61     

Gold Supported on Oxide Surfaces: Environmental Effects as Studied by STM

This paper begins by providing a short review of STM studies of gold particles supported on oxide surfaces. Following this, the morphology of Au particles deposited on thin FeO(111) films at elevated pressures of CO, O₂, CO+O₂, and H₂ has been examined using in situ STM at room temperature. The Au particles are found to be quite stable in oxygen and hydrogen environments at pressures up to 2 mbar. However, in CO and CO+O₂ atmospheres, the destabilization of Au particles located at the step edges occurs leading to the formation of mobile Au species, which migrate across the oxide surface. General problems encountered with high-pressure STM studies are discussed, and data clearly showing the effects of ambient gas impurities is provided. These effects may lead to erroneous conclusions, particularly about morphological changes of and CO dissociation on the gold surfaces at elevated pressures.     

Investigation of 3,3′,5,5′-tetra-tert-butyl-4,4′-stilbenequinone-based catalyst in the reaction of liquid-phase oxidation of inorganic sulfides

In this paper, the intermediate and final reaction products of catalytic oxidation of inorganic sulfides in the presence of oxygen dissolved in the kerosene fraction and 3,3′,5,5′-tetra-tert-butyl-4,4′-stilbenequinone were investigated. The thiosulfate and sulfate are major products of the oxidation of sodium sulfide under these conditions. The intermediate and final products in the catalytic oxidation of sulfide sulfur do not affect the rate of its oxidation. The yield of catalytic oxidation products depends on the nature of the sulfide and on the pH of the solution. The catalytic cycle for sulfide oxidation in the presence of 3,3′,5,5′-tetra-tert-butyl-4,4′-stilbenequinone is shown. The role of 3,3′,5,5′-tetra-tert-butyl-4,4′-stilbenequinone is to create a new and a more effective way of electron transfer from the reducing agent (sulfide) to the oxidant (oxygen).