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46 The PCB Design Magazine • November 2014 face. Included in this topology are any termina- tions. • Stackup planning and the PDN analysis of a PCB are the two main factors that control the stability of a design. In Part 3 next month, I will continue to dis- cuss signal integrity, in particular where most designers go wrong with signal integrity and how to avoid the common pit-falls. PCBDESIGN References 1. Barry Olney: Beyond Design: Practical Sig- nal Integrity, Beyond Design: Pre-Layout Simu- lation, Intro to Board-Level Simulation and the PCB Design Process, Beyond Design: Impedance Matching: Terminations 2. Howard Johnson: High-Speed Signal Propagation 3. Henry Ott: Electromagnetic Compatibil- ity Engineering 4. The ICD Stackup and PDN Planner are distributed globally by Barry olney is managing direc- tor of in-Circuit Design Pty ltd (iCD), australia. This PCB design service bureau specializes in board-level simulation, and has developed the iCD stackup Plan- ner and iCD PDN Planner software. To read past columns, or to contact olney, click here. SIGNAL INTEGRITY, PART 2 continues beyond design by Real Time with... NEPCON South China a team led by the lawrence livermore scien- tists has created a new kind of ion channel based on short carbon nanotubes, which can be insert- ed into synthetic bilayers and live cell membranes to form tiny pores that transport water, protons, small ions, and DNa. These carbon nanotube "porins" have signifi- cant implications for future health care and bio- engineering applications. Nanotube porins even- tually could be used to deliver drugs to the body, serve as a foundation of novel biosensors and DNa sequencing applications, and be used as components of synthetic cells. "Many good and efficient drugs that treat diseases of one organ are quite toxic to another," said aleksandr Noy, an llNl biophysicist who led the study and is the senior author on the paper appearing in Nature. "This is why delivery to a particular part of the body and only releasing it there is much better." The lawrence livermore team, together with colleagues at the Molecular Foundry at the law- rence Berkeley National laboratory, university of California Merced and Berkeley campuses, and university of Basque Country in spain created a new type of a much more efficient, biocompat- ible membrane pore channel out of a carbon nanotube (CNT)--a straw-like molecule that con- sists of a rolled up graphene sheet. "Taken together, our findings establish CNT porins as a promising prototype of a synthetic membrane channel with inherent robustness toward biological and chemical challenges and exceptional biocompatibility that should prove valuable for bionanofluidic and cellular interface applications," said Jia geng, a postdoc who is the first co-author of the paper. Kyunghoon Kim, a postdoc and another co- author, added: "We also expect that our CNT po- rins could be modified with synthetic 'gates' to dramatically alter their se- lectivity, opening up excit- ing possibilities for their use in synthetic cells, drug delivery and biosensing." Tiny Carbon Nanotube Pores Make Big Impact

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