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The influence of quenched disorder on the critical behavior of superfluid He is studied by confinement of the helium to the pores of three diflerent porous media: Vycor, xerogel, and aerogel glasses. In each case a well defined power-law behavior for the superfluid density is observed as the transition temperature is approached. In Vycor the superfluid critical exponent is bulklike, whereas strikingly diff'erent critical exponents are seen in the other two media.

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For electrons tunneling between parallel two-dimensional electron systems, conservation of in-plane momentum produces sharply resonant currentvoltage characteristics and provides a uniquely sensitive probe of the underlying electronic spectral functions. We report here the application of this

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