The radiative decay of metastable 1 s 22s '2p 4 ISO atomic oxygen atoms has been shown to proceed at a rate depending linearly on the concentration of argon or xenon present in the gas mixture. With increasing pressure, the IDrISo atomic line at 5577 A becomes accompanied by a broad emission region identified as a band system of a weakly bound rare-gas oxide molecule. Changes in the transition probability as a function of pressure were measured by using the spin-forbidden ) P I_I So transition at 2972 A as a pressure-independent monitor of the 0(' S) concentration. The observed pressure dependence of the emission probability may be described by rate constants for induced emission in argon and xenon atmospheres: (1) for emission in a bandwidth of + 1.6 A centered on the atomic line at 5577 A, k(Ar)=(7±3)XIO-20 em) seC I, k(Xe)=(3±2)XIO-I9 cm 3 sec-I ;and (2) for emission into the entire green band system, k(Ar)=(3.0+.2)XIO-I8 em) sec-I, k(Xe)=(1.7±.2)x 10-15 em) sec-I. Comparison is made with rate constants for deactivation of these metastable atoms by the same rare gases. It appears that substantially all of the collision-induced emission comes from bound rare-gas oxide molecules whose dissociation equilibria provide the observed pressure dependence.

In fractures where surface fluctuations are large compared to their aperture (narrow fractures), the flow is forced to move in tortuous paths that produce additional viscous friction and are subject to inertia effects. We consider the relation between the magnitude of surface roughness and the onset of inertial effects in the pressure driving the flow through a single open fracture. We performed experiments systematically varying the average aperture of the open fracture and covering a wide range of Reynolds numbers. For each aperture, we analyze the data in terms of the Forchheimer equation and show that the critical Reynolds number, defined as the Reynolds number at which inertial effects contribute 10% of the total pressure losses, is highly correlated with the roughness of the surface. In particular, we show that significant inertial effects appear earlier as the relative importance of surface roughness increases. Finally, we present results showing that the magnitude of the deviations in the pressure field compared to a linear profile, taken at different points in the fracture along the flow direction, is directly related to the relative surface roughness of the fracture.

A fast method and compact device for mixing sub-microliter fluid samples contained in glass capillaries is presented. The fluid is rapidly moved back and forth by air volume displacement driven by a piezo-ceramic actuator. Rapid mixing of different fluids is achieved via diffusion between the main fluid volume in the capillary and the thin fluid film it deposits on the capillary wall through its motion. Bubbles in the fluid are processed out of the capillary by use of an asymmetric velocity profile. A simple analysis model is used to optimize the design of the device and to elucidate the mechanisms involved in mixing. The mixing time is found to be inversely proportional to the fraction of the fluid volume that is left in the film layer for each cycle, which is determined by the wetting properties and the viscosity. The mixing time is therefore controlled by the dead-air volume of the system, the fluid volume, the capillary size, and the displacement limits of the piezo-ceramic actuator, in addition to the intrinsic properties of the fluid being mixed. The device described can mix two 1 μl water solutions in under 3 s. The possible shear breakage of DNA in solution is investigated, and λ-DNA is found to remain intact at aggressive mixing parameters. No evidence of aerosol contamination in polymerase chain reaction reactions was found to date.

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The Genomation Laboratory in the Electrical Engineering Department at the University of Washington has been developing an automated, high-throughput submicroliter-scale reaction preparation system for use in molecular biology, especially as part of the Human Genome Project and other high-throughput DNA sequencing endeavors. Small glass capillaries enable the preparation, handling and monitoring of one-microliter reaction volumes. The Genomation Laboratory, with corporate partners Orca Photonic Systems, Inc. and Engineering Arts, has developed modules for aspiration, dispensing, mixing, transport and rapid thermal treatment of biological samples contained in glass capillaries. The "ACAPELLA 1K" is the first integration of these modules, designed to process 1, OOO samples in an 8-hour day. It has served as a test bed for the technologies as well as for performing biological experiments in conjunction with the University of Washington Genome Center. The Genomation Laboratory is presently developing the next-stage "ACAPELLA 5K" system based on the results of the ACAPELLA 1K system

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