Two papers of note from this week's issue of PNAS (subscribers only):
The use of oscillatory signals in the study of genetic networks
Ovidiu Lipan and Wing H. Wong
The structure of a genetic network is uncovered by studying its response to external stimuli (input signals). We present a theory of propagation of an input signal through a linear stochastic genetic network. We found that there are important advantages in using oscillatory signals over step or impulse signals and that the system may enter into a pure fluctuation resonance for a specific input frequency.
Controlled fabrication of hierarchically branched nanopores, nanotubes, and nanowires
Guowen Meng, Yung Joon Jung, Anyuan Cao, Robert Vajtai, and Pulickel M. Ajayan
Here, we report a generic synthetic approach to rationally design multiply connected and hierarchically branched nanopores inside anodic aluminum oxide templates. By using these nanochannels, we controllably fabricate a large variety of branched nanostructures, far more complex than what exists today. These nanostructures include carbon nanotubes and metallic nanowires having several hierarchical levels of multiple branching. The number and frequency of branching, dimensions, and the overall architecture are controlled precisely through pore design and templated assembly. The technique provides a powerful approach to produce nanostructures of greater morphological complexity, which could have far-reaching implications in the design of future nanoscale systems.