Micromachining technology was used to prepare chemical analysis systems on glass chips (1 centimeter by 2 centimeters or larger) that utilize electroosmotic pumping to drive fluid flow and electrophoretic separation to distinguish sample components. Capillaries 1 to 10 centimeters long etched in the glass (cross section, 10 micrometers by 30 micrometers) allow for capillary electrophoresis-based separations of amino acids with up to 75,000 theoretical plates in about 15 seconds, and separations of about 600 plates can be effected within 4 seconds. Sample treatment steps within a manifold of intersecting capillaries were demonstrated for a simple sample dilution process. Manipulation of the applied voltages controlled the directions of fluid flow within the manifold. The principles demonstrated in this study can be used to develop a miniaturized system for sample handling and separation with no moving parts.

The feasibility of miniaturizing a chemical analysis system on a planar substrate has been demonstrated for a system utilizing

By using the ATLAS detector, observations have been made of a centrality-dependent dijet asymmetry in the collisions of lead ions at the Large Hadron Collider. In a sample of lead-lead events with a per-nucleon center of mass energy of 2.76 TeV, selected with a minimum bias trigger, jets are reconstructed in fine-grained, longitudinally segmented electromagnetic and hadronic calorimeters. The transverse energies of dijets in opposite hemispheres are observed to become systematically more unbalanced with increasing event centrality leading to a large number of events which contain highly asymmetric dijets. This is the first observation of an enhancement of events with such large dijet asymmetries, not observed in proton-proton collisions, which may point to an interpretation in terms of strong jet energy loss in a hot, dense medium.

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2097Micromachined capillary electrophoresis systems with integrated sample injection have been fabricated on glass chips using standard photolithographic and etching techniques. The injector permits volume-defined electrokinetic sample injection without sample biasing. Utilization of short separation capillaries and high field strengths in combination with a small sample plug length results in both fast and efficient separations of fluorescein isothiocyanate-(FITC-) labeled amino acids. Analysis times range from a few seconds to a few tens of seconds with corresponding plate numbers of 5800-160 000, respectively. Plate heights down to 0.3 pm have been obtained using a separation length of 24 mm and an electric field of 1 kV/cm. As it turns out, a maximum separation efficiency has been reached, limited only by diffusion and the effects of both injection and detection. Automated repetitive sample injection and separation on a time scale of seconds is demonstrated and provides a route to quasi-continuous on-line monitoring of chemical species in a sensorlike fashion.