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We give examples of string compactifications to 4d Minkowski space with different amounts of supersymmetry that can be connected by spherical domain walls. The tension of these domain walls is tunably lower than the 4d Planck scale. The "stringy" description of these walls is known in terms of certain configurations of wrapped Dirichlet and NS branes. This construction allows us to connect a variety of vacua with 4d N = 4, 3, 2, 1 supersymmetry.

Viseoelastie properties of bitumens in eontinuous and eyelie deformationA. I. I s a y e v , V. A. Z o l o t a r e v , and G. V V i n o g r a d o v With 13 figures and 2 tables (

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Recent investigations showed that the THz photoresponse of quantum Hall systems (QHS) is a complex combination of different mechanisms. In this work, we separate these parts by varying the electron concentration and the source-drain current. For our photoconductivity measurements, we used a pulsed p-Ge cyclotron laser as a monochromatic THz radiation source and changed the magnetic field, the source-drain current and the electron concentration (via a backgate) of the QH sample. The spectral resolution of the QHS was found to improve with increasing values of the source-drain current up to the breakdown of the QH effect.