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of the catalyst, including selectivity for the
case of more complex catalytic pathways.
Figure 2B suggests the local regeneration of
deactivated areas as one possible starting
point for such a design.
In the case of island- forming reactants, for which the reaction oc- curs at the perimeter of these islands (34,35), the generation of additional boundaries should enhance reaction rates.
What are good feedback laws for these objectives, and how can they be implemented? Hierarchical con- trol schemes (36 ) may be key to the practical implementation of real-time feedback with finely distributed actuation. References and Notes1.
Lundqvist et al.,Proc.
95, 10356 (1998). 2.
Eng. 38, 1 (1996). 3.
Somorjai, Langmuir 14, 1458 (1998). 4.
Kasemo, Faraday Discuss., 105, 237 (1996). 5.
Srinivasan et al.,AIChE J.
43, 3059 (1997). 6.
Lin et al.,Phys.
84, 4240 (2000). 7.
Showalter, Nature 361, 240 (1993). 8.
Kim et al.,Science 292, 1357 (2001). 9.
Rep.29, 265 (1997). 10. iiii , W.
Ertl, Nature343, 355 (1990). 11.
65, 3013 (1990). 12.
Imbihl, Nature370, 124 (1994). 13.
Graham et al.,Science 264, 80 (1994). 14.
Lauterbach et al.,Physica D 123, 493 (1998). 15.
Schu¬ tz, R.
83, 2857 (1999). 16.
121, 480 (1997). 17.
Esch et al.,Catal.
52, 85 (1998). 18.
74, 566 (1996). 19.
Eng.24, 139 (2000). 20.
Ka «da«r, J.
Showalter, Nature391, 770 (1998). 21.
Mu¬ ller, Nature366, 322 (1993). 22.
Sontag, Mathematical Control Theory: Determin- istic Finite-Dimensional Systems (Springer-Verlag, Berlin, ed.
2, 1998). 23.
Lett.64, 1196 (1990). 24.
Mu¬ ller, Phys.
78, 3398 (1997). 25.
Soc. 45, 46 (2000). 26.
Thornburg Jr., Phys.
Lett.72, 2009 (1994). 27.
Epstein, Nature406, 389 (2000). 28.
Desired spatiotemporal heating patterns could be programmed into the control computer by using LabVIEW.
In addition, it was possible to control the laser spot on the surface by hand directly, using the computer mouse.
This joystick mode establishesÑas in computer games or ßight simulatorsÑa direct feedback with the human brain as image processor and control action calculator.
For our computer-con- trolled feedback experiments, real-time image pro- cessing and desired rules for the heating patterns and intensities were implemented in software. 29.
Schu¬ tze, S.
Mu¬ ller, Phys.
Lett. 68, 248 (1992). 30.
121, 8065 (1999). 31.
In our experiments, the Pt(110) single-crystal sam- ple was kept in an ultrahigh-vacuum apparatus. The surface was prepared by Ar-ion sputtering and annealing to about 1100 K.
The quality of the surface preparation was checked with low-energy electron diffraction. 32.
Ertl, Science 270, 608 (1995). 33.
We have measured the spatiotemporal temperature proÞle of our laser spot using a cooled infrared (IR) camera with a temperature resolution of 0.05 K at room temperature.
From those IR images we deduced a maximum differential temperature rise at the spot of about 15 K; typically, we worked at powers giving a temperature rise of 2 to 3 K over an area of ;80 mm in diameter.
Detailed heat balance simulations, including radiation and conduction, showed that only 5 ms were needed to locally establish this differential temperature rise, conÞrming our experimental obser- vation of a heat quench in less than 20 ms.
In other words, the temperature rises and returns to its back- ground state essentially instantaneously with the movement of the laser spot. 34.
Vo¬ lkening, J.
Phys.114, 6382 (2001). 35.
Sci.38, 719 (1983). 36.
Sastry, IEEE Trans. Autom.
Control 45, 1144 (2000). 37.
Graham et al.,Phys.
E 52, 76 (1995). 38.
We gratefully acknowledge partial support by the OfÞce of Naval Research (I.G.K.
and H.H.R.), NSF, Air Force OfÞce of ScientiÞc Research, and the Humboldt Foundation (I.G.K.), and by a Marie Curie Fellowship (A.G.P.) under contract HPMFCT-2000-00685.
We thank M.
Pollmann for the measurement of Fig.
1C and S.
Shvartsman for many discussions. 19 June 2001; accepted 28 August 2001 Submicrometer Metallic Barcodes Sheila R.
Nicewarner-Pen ÷a, 1R.
GrifÞth Freeman, 2 Brian D.
Reiss, 1Lin He, 2David J.
Pen÷a, 1Ian D.
Walton, 2 Remy Cromer, 2Christine D.
Keating, 1* Michael J.
Natan 2* We synthesized multimetal microrods intrinsically encoded with submicrome- ter stripes.
Complex striping patterns are readily prepared by sequential elec- trochemical deposition of metal ions into templates with uniformly sized pores. The differential reßectivity of adjacent stripes enables identiÞcation of the striping patterns by conventional light microscopy.
This readout mechanism does not interfere with the use of ßuorescence for detection of analytes bound to particles by afÞnity capture, as demonstrated by DNA and protein bioassays. Multiplexing and miniaturization are becom- ing pervasive themes in bioanalysis.
The push to measure ever-increasing numbers of species from smaller and smaller sample vol- umes has led to innovative devices for sample manipulation [e.g., chip-based microfluidics (1)] and ingenious approaches to simulta- neous measurement capabilities (e.g., mi- Fig.
1. Synthesis of barcoded particles. REPORTS www.sciencemag.org SCIENCE VOL 294 5 OCTOBER 2001 137 on March 20, 2013 www.sciencemag.org Downloaded from. »
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